Isolation, culture and immortalisation of hepatic oval cells from adult mice fed a choline-deficient, ethionine-supplemented diet

Oval cells have great potential for use in cell therapy to treat liver disease, however this cannot be achieved until the factors which govern their proliferation and differentiation are better understood. We describe a method to establish primary cultures of murine oval cells, and the derivation of two novel lines from these. Primary cultures from the livers of wildtype or TAT-GRE lacZ transgenic mice subjected to a choline-deficient, ethionine-supplemented diet comprised up to 80% oval cells at day 7 based on A6 or CK19 staining. Cell lines were clonally derived, which underwent spontaneous immortalisation following prolonged maintenance in culture. Immunostaining and RT-PCR demonstrated they express hepatocytic and biliary markers and they were therefore termed “bipotential murine oval liver” (BMOL) cells. Under proliferating culture conditions, BMOL or BMOL-TAT cells abundantly expressed oval cell and biliary markers, whereas mature hepatocytic markers were upregulated when the growth conditions were changed to facilitate differentiation. Hepatic differentiation of BMOL-TAT cells could be traced by measuring the expression of their lacZ transgene, which is driven by a promoter element from tyrosine aminotransferase (TAT), a marker of adult hepatocytes. Interestingly, haematopoietic markers were upregulated in superconfluent cultures, indicating a possible multipotentiality. None of the cell lines grew in semi-solid agar, nor did they form tumours in nude mice, suggesting they are non-tumourigenic.

These novel murine oval cell lines, together with a reliable method for isolation and culture of primary oval cells, will provide a useful tool for investigating the contribution of oval cells to liver regeneration.     

Modulation of calcium by the carcinogenic process in the liver induced by a choline-deficient diet

A diet devoid of choline and low in methionine (CD), without any added carcinogen, has been shown to induce 100% preneoplastic nodules and more than 50% cancer in the rat liver. Attempts to understand the mechanism by which a CD diet induces liver cell cancer revealed that like chemical carcinogens, a CD diet also appears to cause alterations in DNA, perhaps mediated by free radicals. Indeed, a CD diet induces nuclear lipid peroxidation prior to the changes in DNA. The CD diet induced DNA alterations coupled with continuing liver cell proliferation may account for the induction of initiated hepatocytes by the CD diet. To gain insight into the nature of free radicals generated by the CD diet, experiments were designed to determine whether agents that modulate free radical effects influence the CD diet induced changes in the liver. We investigated the effect of Ca2+ in the modulation of CD diet induced alterations in the liver. The results show that extra Ca2+ when added to the CD diet prevented some of the early changes due to choline deficiency, such as nuclear lipid peroxidation and DNA damage, but had little or no effect on the triglyceride accumulation in the liver. Also, the same CD diet with extra Ca2+, when used as a promoter after initiation by diethylnitrosamine, decreased the number and size of early putative preneoplastic foci and nodules.     

Differential alterations in mitochondrial function induced by a choline-deficient diet: understanding fatty liver disease progression

Non-alcoholic fatty liver disease (NAFLD) is an increasingly reported pathology, characterized by fat accumulation within the hepatocyte. Growing evidences suggest specific effects on mitochondrial metabolism, but it is still unclear the relationship between fatty liver progression and mitochondrial function. In the present work we have investigated the impact of fatty liver on mitochondrial bioenergetic functions and susceptibility to mitochondrial permeability transition (MPT) induction in animals fed a choline-deficient diet (CDD) for 4, 8, 12 or 16 weeks. Mitochondria isolated from CDD animals always exhibited higher state 4 respiration. Mitochondrial membrane potential was decreased in CDD animals at 4 and 16 weeks. At 12 weeks, oxidative phosphorylation was more efficient in CDD animals, suggesting a possible early response trying to revert the deleterious effect of increased triglyceride storage in the liver. However, mitochondrial dysfunction was evident in CDD animals at 16 weeks as indicated by decreased RCR and ADP/O, with a corresponding decrease in respiratory chain enzymes activities. Such loss of respiratory efficiency was associated with accumulation of protein oxidation products, in tissue and mitochondrial fraction. Additionally, although no differences in ATPase activity, the lag phase was increased in mitochondria from CDD animals at 16 weeks, associated with decreased content of the adenine nucleotide translocator. Increased susceptibility to calcium-induced MPT was evident in CDD animals at all time points. These results suggest a dynamic mechanism for the development of NALFD associated with altered mitochondrial function.     

Mitochondrial adaptations to steatohepatitis induced by a methionine- and choline-deficient diet

Nonalcoholic fatty liver disease (NAFLD) has become common liver disease in Western countries. There is accumulating evidence that mitochondria play a key role in NAFLD. Nevertheless, the mitochondrial consequences of steatohepatitis are still unknown. The bioenergetic changes induced in a methionine- and choline-deficient diet (MCDD) model of steatohepatitis were studied in rats. Liver mitochondria from MCDD rats exhibited a higher rate of oxidative phosphorylation with various substrates, a rise in cytochrome oxidase (COX) activity, and an increased content in cytochrome aa3. This higher oxidative activity was associated with a low efficiency of the oxidative phosphorylation (ATP/O, i.e., number of ATP synthesized/natom O consumed). Addition of a low concentration of cyanide, a specific COX inhibitor, restored the efficiency of mitochondria from MCDD rats back to the control level. Furthermore, the relation between respiratory rate and protonmotive force (in the nonphosphorylating state) was shifted to the left in mitochondria from MCDD rats, with or without cyanide. These results indicated that, in MCDD rats, mitochondrial ATP synthesis efficiency was decreased in relation to both proton pump slipping at the COX level and increased proton leak although the relative contribution of each phenomenon could not be discriminated. MCDD mitochondria also showed a low reactive oxygen species production and a high lipid oxidation potential. We conclude that, in MCDD-fed rats, liver mitochondria exhibit an energy wastage that may contribute to limit steatosis and oxidative stress in this model of steatohepatitis.     

Pioglitazone prevents hepatic steatosis, fibrosis, and enzyme-altered lesions in rat liver cirrhosis induced by a choline-deficient L-amino acid-defined diet

Non-alcoholic steatohepatitis (NASH) may progress to liver cirrhosis, and NASH patients with liver cirrhosis have a risk of development of hepatocellular carcinoma. Peroxisome proliferator-activated receptor (PPAR) gamma ligand has recently been reported to have improved the condition of patients with NASH. The aim of this study was to investigate whether pioglitazone, a PPARgamma ligand, has any influence on the animal model of NASH as well as isolated hepatic stellate cells. In vivo, the effects of pioglitazone were examined using the choline-deficient L-amino acid-defined (CDAA)-diet liver fibrosis model. After two weeks, pioglitazone improved hepatic steatosis, prevented liver fibrosis, and reduced preneoplastic lesions in the liver after 10 weeks. Pioglitazone reduced the expression of TIMP-1 and TIMP-2 mRNA without changing MMP-13 mRNA expression compared to the liver fed a CDAA diet alone. In vitro, pioglitazone prevented the activation of hepatic stellate cells resulting in reducing the expression of type I procollagen, MMP-2, TIMP-1, and TIMP-2 mRNA with increased MMP-13 mRNA expression. These results indicate that pioglitazone may be one of the candidates for the benefit drugs for the liver disease of patients with NASH.     

CD117+ stem cells play a key role in therapeutic angiogenesis induced by bone marrow cell implantation

Therapeutic angiogenesis can be induced by the implantation of bone marrow mononuclear cells. We investigated the roles of mature mononuclear cell and stem cell fractions in bone marrow in this treatment. Although CD34 is the most popular marker for stem cell selection for inducing therapeutic angiogenesis, we separated CD117-positive cells (CD117+) from mature bone marrow mononuclear cells [CD117-negative cells (CD117-)] from mice using the antibody to the stem cell receptor, because some of the bone marrow stem cells that express CD117+ and CD34- might generate angiogenic cytokines and differentiate into endothelial cells. The angiogenic potency of CD117+ and CD117- cells was investigated in vitro and in vivo. Significantly higher levels of VEGF were secreted from the CD117+ cells than from the CD117- cells (P < 0.001). Most of the CD117- cells died, but the CD117+ cells grew well and differentiated into endothelial cells within 14 days of culture. The CD117+ cells survived and were incorporated in microvessels within 14 days of being implanted into the ischemic hindlimbs of mice, but the CD117- cells did not. The microvessel density and blood perfusion of the ischemic hindlimbs were significantly higher in the CD117+ cell-implanted mice than in the CD117- cell-implanted mice (P < 0.01). The microvessel density in ischemic hindlimbs was also significantly higher in the CD117+ cell-implanted mice than in the total bone marrow cell-implanted mice (P < 0.05). Thus CD117+ stem cells play a key role in the therapeutic angiogenesis induced by bone marrow cell implantation.     

Telmisartan prevents hepatic fibrosis and enzyme-altered lesions in liver cirrhosis rat induced by a choline-deficient L-amino acid-defined diet

Rennin-angiotensin system is involved in liver fibrogenesis through activating hepatic stellate cells (HSCs). Telmisartan (Tel) is an angiotensin II type 1 receptor antagonist, could function as a selective peroxisome proliferator-activated receptor γ activator. Here we studied the effect of Tel on liver fibrosis, pre-neoplastic lesions in vivo and primary HSCs in vitro. In vivo study, we used the choline-deficient l-amino acid-defined (CDAA)-diet induced rat NASH model. The rats were fed the CDAA diet for 8 weeks to induce liver fibrosis and pre-neoplastic lesions, and then co-administrated with Tel for another 10 weeks. Tel prevented liver fibrogenesis and pre-neoplastic lesions by down-regulating TGFβ1 and TIMP-1, 2 and increasing MMP-13 expression. Tel inhibited HSCs activation and proliferation. These results suggested that Tel could be a promising drug for NASH related liver fibrosis.     

HSCs play a distinct role in different phases of oval cell-mediated liver regeneration

Hepatic stem cell niche plays an important role in hepatic oval cell-mediated liver regeneration. As a component of hepatic stem cell niche, the role of hepatic stellate cells (HSCs) in oval cell proliferation needs further studies. In the present study, we isolated HSCs from rats at indicated time point after partial hepatectomy (PH) in 2-acetylaminofluorene/PH oval cell proliferation model. Conditional medium (CM) from HSCs were collected to detect their effects on proliferation and the mitogen-activated protein kinase pathway activation of two oval cell lines. We found that CM collected from HSCs at early phase of liver regeneration (4 and 9?days group) contained high levels of hepatocyte growth factor (HGF) and stimulated oval cell proliferation via extracellular signal-regulated kinase and p38 pathway. CM collected from HSCs at terminal phase of liver regeneration (12 and 15?days group) contained high levels of transforming growth factor (TGF)-β1, which suppressed DNA synthesis of oval cells. The shift between these two distinct effects depended on the balance between HGF and TGF-β1 secreted by HSCs. Our study demonstrated that HSCs acted as a positive regulator at the early phase and a negative regulator at the terminal phase of the oval cell-mediated liver regeneration. Copyright ? 2012 John Wiley & Sons, Ltd.     

Adaptation of subcellular glutathione detoxification system to stress conditions in choline-deficient diet induced rat fatty liver

The response of fatty liver to stress conditions (t-butyl hydroperoxide [t-BH] or 36 h of fasting) was investigated by assessing intracellular glutathione (GSH) compartmentation and redox status, GSH peroxidase (GSH-Px) and reductase (GSSG-Rx) activities, lipid peroxidation (TBARs) and serum ALT levels in rats on a choline-deficient diet. Baseline cytosolic GSH was similar between fatty and normal livers, while the mitochondrial GSH content was significantly lower in fatty livers. With the except of cytosolic GSH-Px activity, steatosis was associated with significantly higher GSH-related enzymes activities. Liver TBARs and serum ALT levels were also higher. Administration of t-BH significantly decreased the concentration of cytosolic GSH, increased GSSG levels in all the compartments, and increased TBARs levels in cytosol and mitochondria and serum ALT; all these alterations were more marked in rats with fatty liver. Fasting decreased the concentration of GSH in all the compartments both in normal and fatty livers, increased GSSG, TBARs and ALT levels, and decreased by 50% the activities of GSH-related enzymes. Administration of diethylmaleimide (DEM) resulted in cytosolic and microsomal GSH pool depletion. Administration of t-BH to DEM-treated rats further affected cytosolic GSH and enhanced ALT levels, whereas the application of fasting to GSH depleted rats mainly altered the mitochondrial GSH system, especially in fatty livers. This study shows that fatty livers have a weak compensation of hepatic GSH regulation, which fails under stress conditions, thus increasing the fatty liver's susceptibility to oxidative damage. Differences emerge among subcellular compartments which point to differential adaptation of these organelles to fatty degeneration.     

Dimethylethanolamine does not prevent liver failure in phosphatidylethanolamine N-methyltransferase-deficient mice fed a choline-deficient diet

Mice that lack phosphatidylethanolamine-N-methyltransferase (PEMT) and are fed a choline-deficient (CD) diet suffer severe liver damage and do not survive. Since phosphatidyldimethylethanolamine (PDME) has physical properties similar to those of phosphatidylcholine (PC), we hypothesized that dimethylethanolamine (DME) would be converted into PDME that might substitute for PC, and therefore abrogate the liver damage in the Pemt -/- mice fed a CD diet. We fed Pemt -/- mice either a CD diet, a CD diet supplemented with choline, or a CD diet supplemented with DME (CD + DME). Pemt -/- mice fed the CD diet developed severe liver failure by 4 days while CD + DME-fed mice developed severe liver failure by 5 days. The hepatic PC level in choline-supplemented (CS) mice was 67 +/- 4 nmol/mg protein, whereas the PC content was reduced in CD- and CD + DME-fed mice (49 +/- 3 and 30 +/- 3 nmol/mg protein, respectively). Upon supplementation of the CD diet with DME the amount of hepatic PDME was 81 +/- 9 nmol/mg protein so that the hepatic content of PC + PDME combined was 111 nmol/mg protein. Moreover, plasma apolipoprotein B100 and Al levels were markedly lower in mice fed the CD + DME diet compared to mice fed the CS diet, as was the plasma content of PC. Thus, despite replacement of the deficit in hepatic PC with PDME in Pemt -/- mice fed a CD diet, normal liver function was not restored. We conclude that although PC and PDME exhibit similar physical properties, the three methyl groups of choline are required for hepatic function in mice.     

Oxidative stress in the pathogenesis of nonalcoholic fatty liver disease,in rats fed with a choline-deficient diet

Background/Aim : The pathogenesis of Nonalcoholic Fatty Liver Disease remains largely unknown, but oxidative stress seems to be involved. The aim of this study was to evaluate the role of oxidative stress in experimental hepatic steatosis induced by a choline-deficient diet. Methods : Fatty liver disease was induced in Wistar rats by a choline-deficient diet. The animals were randomized into three groups: I (G1) and II (G2), n=6 each - fed with a choline-deficient diet for four and twelve weeks respectively; Group III (control-G3; n=6) - fed with a standard diet for twelve weeks. Samples of plasma and liver were submitted to biochemical, histological and oxidative stress analysis. Variables measured included serum levels of aminotransferases (AST, ALT), cholesterol and triglycerides. Oxidative stress was measured by lucigenin-enhanced luminescence and the concentration of hydroperoxides (CE-OOH-cholesteryl ester) in the liver tissue. Results: We observed moderate macro- and microvesicular fatty change in periportal zones G1 and G2 as compared to controls (G3). In G2, fatty change was more severe. The inflammatory infiltrate was scanty and no fibrosis was seen in any group. There was a significant increase of AST and triglycerides in G1 and G2 as compared to control group G3. The lucigenin-amplified luminescence (cpm/mg/min × 10³) was significantly increased in G1 (1393±790) and G2 (7191±500) as compared to controls (513±170), p <0.05. The concentrations of CE-OOH were higher in G1 (5.7±0.9 nmol/mg protein) as compared to control (2.6±0.7 nmol/mg protein), p <0.05. Conclusion: 1) Oxidative stress was found to be increased in experimental liver steatosis; 2) The production of reactive oxygen species was accentuated when liver steatosis was more severe; 3) The alterations produced by oxidative stress could be an important step in the pathogenesis of nonalcoholic fatty liver disease.     

Bone marrow stromal cells, preadipocytes, and dermal fibroblasts promote epidermal regeneration in their distinctive fashions

Mesenchymal cell types, under mesenchymal-epithelial interaction, are involved in tissue regeneration. Here we show that bone marrow stromal cells (BMSCs), subcutaneous preadipocytes, and dermal fibroblasts distinctively caused keratinocytes to promote epidermal regeneration, using a skin reconstruction model by their coculture with keratinocytes. Three mesenchymal cell types promoted the survival, growth, and differentiation of keratinocytes, whereas BMSCs and preadipocytes inhibited their apoptosis. BMSCs and preadipocytes induced keratinocytes to reorganize rete ridge- and epidermal ridge-like structures, respectively. Keratinocytes with fibroblasts or BMSCs expressed the greatest amount of interleukin (IL)-1alpha protein, which is critical for mesenchymal-epithelial cross-talk in skin. Keratinocytes with or without three mesenchymal supports displayed another cross-talk molecule, c-Jun protein. Without direct mesenchymal-epithelial contact, the rete ridge- and epidermal ridge-like structures were not replicated, whereas the other phenomena noted above were. DNA microarray analysis showed that the mesenchymal-epithelial interaction affected various gene expressions of keratinocytes and mesenchymal cell types. Our results suggest that not only skin-localized fibroblasts and preadipocytes but also BMSCs accelerate epidermal regeneration in complexes and that direct contact between keratinocytes and BMSCs or preadipocytes is required for the skin-specific morphogenesis above, through mechanisms that differ from the IL-1alpha/c-Jun pathway.     

Role of white adipose lipolysis in the development of NASH induced by methionine- and choline-deficient diet

Methionine- and choline-deficient diet (MCD) is a model for nonalcoholic steatohepatitis (NASH) in rodents. However, the mechanism of NASH development by dietary methionine/choline deficiency remains undetermined. To elucidate the early metabolic changes associated with MCD-NASH, serum metabolomic analysis was performed using mice treated with MCD and control diet for 3 days and 1  week, revealing significant increases in oleic and linoleic acids after MCD treatment. These increases were correlated with reduced body weight and white adipose tissue (WAT) mass, increased phosphorylation of hormone-sensitive lipase, and up-regulation of genes encoding carboxylesterase 3 and β2-adrenergic receptor in WAT, indicating accelerated lipolysis in adipocytes. The changes in serum fatty acids and WAT by MCD treatment were reversed by methionine supplementation, and similar alterations were detected in mice fed a methionine-deficient diet (MD), thus demonstrating that dietary methionine deficiency enhances lipolysis in WAT. MD treatment decreased glucose and increased fibroblast growth factor 21 in serum, thus exhibiting a similar metabolic phenotype as the fasting response. Comparison between MCD and choline-deficient diet (CD) treatments suggested that the addition of MD-induced metabolic alterations, such as WAT lipolysis, to CD-induced hepatic steatosis promotes liver injury. Collectively, these results demonstrate an important role for dietary methionine deficiency and WAT lipolysis in the development of MCD-NASH.     

Hormonal responsiveness of liver cells during the liver regeneration process induced by carbon tetrachloride administration

In control rats most of the ureagenic effect of adrenaline is mediated through alpha1-adrenoceptors with little participation of beta-adrenoceptors. Administration of carbon tetrachloride to rats induces significant changes in the adrenergic responsiveness of their hepatocytes. In rats intoxicated 3-5 days before the experiments were performed there is a marked increase in the beta-adrenergic and a decrease in the alpha-adrenergic responsiveness of the hepatocytes. The alpha1-adrenergic responsiveness increased with time reaching its basal level 15 days after the administration of carbon tetrachloride; simultaneously, the betal-adrenergic responsiveness was decreased. No change in the responsiveness to vasopressin and angiotensin II was observed in intoxicated animals as compared to the controls. In contrast, the responsiveness to glucagon was increased. Increased ability of local anesthetics to decrease urea production was observed in cells from intoxicated animals. It is suggested that changes at the plasma membrane level (lipids, receptors and transducing proteins) might participate in producing these effects.     

Lecithin depletion in liver mitochondria of rats fed a choline-deficient diet. Effect on beta-hydroxybutyrate dehydrogenase

Liver Mitochondria of fasted rats refed a choline-deficient diet have a significantly lower content of lecithins than mitochondria of rats refed a choline supplemented diet. Along with the depletion of lecithins there is a 50% decrease in the activity of β-hydroxybutyrate dehydrogenase, a mitochondrial enzyme which has a specific functional requirement for lecithins. The activity of the enzyme is partially restored by preincubation of the depleted mitochondria with microdispersion of lecithins.     

Hepcidin plays a negative role in liver regeneration

Hepcidin is a key regulator of iron metabolism. The expres- sion of hepcidin is significantly induced by iron overload, inflammation, and infection of pathogens. Recent studies have indicated that the expression of hepcidin in the liver is also regulated during liver regeneration. However, the mechanism of the regulation of hepcidin expression and its role in liver regeneration remain unclear. In this study, we found that the hepatocyte growth factor inhibited hepcidin expression in the liver during the late stage of liver regener- ation. Meanwhile, we investigated the effect of hepcidin on liver regeneration. Mice overexpressing hepcidin-1 exhib- ited impaired hepatic regeneration after partial hepatect- omy, as determined by immunohistochemieal staining of the proliferation cell nuclear antigen. Our results demon- strated a negative role of hepcidin in modulating liver re- generation, and suggested that a sustained high iron level by the down-regulation of hepcidin at the late stage of liver regeneration is required for hepatocyte proliferation.     

Effect of methotrexate on long-chain fatty acid metabolism in liver of rats fed a standard or a defined, choline-deficient diet

The effect of methotrexate on lipids in serum and liver and key enzymes involved in esterification and oxidation of long-chain fatty acids were investigated in rats fed a standard diet and a defined choline-deficient diet. Hepatic metabolism of long-chain fatty acids were also studied in rats fed the defined diet with or without choline. When methotrexate was administered to the rats fed the standard diet there was a slight increase in hepatic lipids and a moderate reduction in the serum level. The palmitoyl-CoA synthetase activity and the microsomal glycerophosphate acyltransferase activity in the liver of rats were increased by methotrexate. The data are consistent with those where the liver may fail to transfer the newly formed triacylglycerols into the plasma with a resultant increase in liver triacylglycerol content and a decrease in serum lipid levels. Fatty liver of methotrexate-exposed rats can not be attributed simply to a reduction of fatty acid oxidation as the carnitine palmitoyltransferase activity was increased. The methotrexate response in the rats fed the defined choline-deficient diet was different. There was a reduction in both serum and hepatic triacylglycerol and the glycerophosphate acyltransferase and palmitoyl-CoA synthetase activities. The carnitine palmitoyltransferase activity was unchanged. Hepatomegaly and increased hepatic fat content, but decreased serum triacylglycerol, total cholesterol and HDL cholesterol were found to be related to the development of choline deficiency as the pleiotropic responses were almost fully prevented by addition of choline to the choline-deficient diet. Addition of choline to the choline-deficient diet normalized the total palmitoyl-CoA synthetase and carnitine palmitoyltransferase activities. In contrast to methotrexate exposure, choline deficiency increased the mitochondrial glycerophosphate acyltransferase activity. The data are consistent with those of where fatty liver induction of choline deficiency may be related to an enhanced esterification of long-chain fatty acids concomitant with a reduction of their oxidation.     

Different mutation patterns of mitochondrial DNA displacement-loop in hepatocellular carcinomas induced by N-nitrosodiethylamine and a choline-deficient l-amino acid-defined diet in rats

Mutations of the mitochondria DNA (mtDNA) displacement loop (D-loop) were investigated to clarify different changes of exogenous and endogenous liver carcinogenesis in rats. We induced hepatocellular carcinomas (HCCs) in rats with N-nitrosodiethylamine (DEN) and a choline-deficient l-amino acid-defined (CDAA) diet. DNAs were extracted from 10 HCCs induced by DEN and 10 HCCs induced by the CDAA diet. To identify mutations in mtDNA D-loop, polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis, followed by nucleotide sequencing, was performed. Mutations were detected in 5 out of 10 HCCs (50%) induced by DEN. Four out of 5 mutations were G/C to A/T transitions at positions 15707, 15717, 15930, and 16087, and one T/A to C/G transition at position 15559. By contrast, no mutations were found in 10 HCCs induced by the CDAA diet. These results demonstrated that mutations in mtDNA D-loop occur in rat HCCs induced by DEN but not by the CDAA diet, suggesting that mtDNA D-loop is a target of exogenous liver carcinogenesis in rats.