Phenotypic stability of adult rat hepatocytes in primary monolayer culture

Rapid changes in chromatin structure during dedifferentiation of primary hepatocytes in vitro

Primary hepatocytes are widely used in the pharmaceutical industry to screen drug candidates for hepatotoxicity, but hepatocytes quickly dedifferentiate and lose their mature metabolic function in culture. Attempts have been made to better recapitulate the in vivo liver environment in culture, but the full spectrum of signals required to maintain hepatocyte function ex vivo remains elusive. To elucidate molecular changes that accompany, and may contribute to dedifferentiation of hepatocytes ex vivo, we performed lineage tracing and comprehensive profiling of alterations in their gene expression profiles and chromatin landscape during culture. First, using genetically tagged hepatocytes we demonstrate that expression of the fetal gene alpha-fetoprotein in cultured hepatocytes comes from cells that previously expressed the mature gene albumin, and not from a population of albumin-negative precursor cells, proving mature hepatocytes undergo true dedifferentiation in culture. Next we studied the dedifferentiation process in detail through bulk RNA-sequencing of hepatocytes cultured over an extended period. We identified three distinct phases of dedifferentiation: an early phase, where mature hepatocyte genes are rapidly downregulated in a matter of hours; a middle phase, where fetal genes are activated; and a late phase, where initially rare contaminating non-parenchymal cells proliferate, taking over the culture. Lastly, to better understand the signaling events that result in the rapid downregulation of mature genes in hepatocytes, we examined changes in chromatin accessibility in these cells during the first 24 h of culture using Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq). We find that drastic and rapid changes in chromatin accessibility occur immediately upon the start of culture. Using binding motif analysis of the areas of open chromatin sharing similar temporal profiles, we identify several candidate transcription factors potentially involved in the dedifferentiation of primary hepatocytes in culture.

Impact of HCV Infection on Hepatocyte Polarity and Plasticity

The hepatitis C virus (HCV) is an oncogenic virus that alters the cell polarization machinery in order to enter the hepatocyte and replicate. While these alterations are relatively well defined, their consequences in the evolution of the disease remain poorly documented. Since 2012, HCV infection can be effectively cured with the advent of direct acting antivirals (DAA). Nevertheless, patients cured of their HCV infection still have a high risk of developing hepatocellular carcinoma (HCC). Importantly, it has been shown that some of the deregulations induced by HCV are maintained despite a sustained virologic response (SVR), including the down-regulation of some hepatocyte functions such as bile acid metabolism, exemplifying cell dedifferentiation, and the up-regulation of the epithelial–mesenchymal transition (EMT). EMT is a process by which epithelial cells lose their differentiation and their specific polarity to acquire mesenchymal cell properties, including migration and extracellular matrix remodeling capabilities. Of note, epithelial cell polarity acts as a gatekeeper against EMT. Thus, it remains important to elucidate the mechanisms by which HCV alters polarity and promotes EMT that could participate in viral-induced hepatic carcinogenesis. In this review, we define the main steps involved in the polarization process of epithelial cells and recall the essential cellular actors involved. We also highlight the particularities of hepatocyte polarity, responsible for their unique morphology. We then focus on the alterations by HCV of epithelial cell polarity and the consequences of the transformation of hepatocytes involved in the carcinogenesis process.

Self-Organized Liver Microtissue on a Bio-Functional Surface: The Role of Human Adipose-Derived Stromal Cells in Hepatic Function

The maintenance of hepatocyte function is a critical research topic in liver tissue engineering. Although an increasing number of strategies have been developed, liver tissue engineering using hepatocytes as a therapeutic alternative remains challenging owing to its poor efficacy. In this study, we developed a multicellular hepatic microtissue to enhance the function of induced hepatic precursor cells. Mouse induced hepatic precursor cells (miHeps) were self-organized in 3D with human adipose-derived stem cells (hASCs) on a bio-functional matrix. We found that hepatic phenotypes, such as levels of albumin, asialoglycoprotein receptor-1, and cytochrome P450, were enhanced in miHeps-hASC microtissue comprising miHeps and hASCs relative to two-dimensional-cultured miHeps-hASCs. Additionally, the secretome of 3D-cultured hASCs increased the hepatic function of mature miHeps. Furthermore, hepatic gene expression was reduced in mature miHeps treated with conditioned media of hypoxia-inducible factor 1α (HIF1α)-depleted hASCs relative to that with conditioned media of control hASCs. Our results suggested that the hepatic function of 3D-co-cultured miHeps could be enhanced by HIF1α-dependent factors secreted from stromal cells. This study provides an insight into the factors regulating hepatic function and shows that self-organized hepatic microtissue could act as liver spheroids for liver regenerative medicine and liver toxicity tests.

The role of cellular interactions in the induction of hepatocyte polarity and functional maturation in stem cell-derived hepatic cells

The unique microenvironment found within the liver in vivo plays a key role in the induction of functional maturation in the developing hepatocyte. During organogenesis, hepatocytes acquire a polar phenotype that allows them to perform their functions of bile production and transport, protein synthesis, metabolism, and detoxification simultaneously, independently, and efficiently. It is thought that the induction of polarity and functional maturation in hepatocytes is dependent on the complex interplay of cell-cell and cell-extracellular matrix (ECM) interactions. While this process is highly efficient in the human liver, it has been shown that hepatocytes rapidly lose their functions when placed in cell culture. This poses a challenge for the development of a bioartificial liver (BAL) support system, which utilizes a live cellular source to perform hepatic functions in the event of acute liver failure or primary nonfunction. However, once the molecular mechanisms underlying the induction of hepatocyte polarity are fully identified, it will be possible to develop highly functional hepatic cells from human pluripotent stem cells (hPSCs). This new cell line would be an ideal cellular source for a BAL system, as it would have both the functionality and longevity to support a patient through the entire clinical course of treatment. In this review, we explore the literature that has examined the potential mechanisms that induce polarity in the developing hepatocyte and discuss the future implications of this knowledge in a clinical setting from a bioengineering perspective.

Astrocyte Elevated Gene-1 Regulates Macrophage Activation in Hepatocellular Carcinogenesis

Chronic inflammation is a known hallmark of cancer and is central to the onset and progression of hepatocellular carcinoma (HCC). Hepatic macrophages play a critical role in the inflammatory process leading to HCC. The oncogene Astrocyte elevated gene-1 (AEG-1) regulates NFκB activation, and germline knockout of AEG-1 in mice (AEG-1-/-) results in resistance to inflammation and experimental HCC. In this study, we developed conditional hepatocyte- and myeloid cell-specific AEG-1-/- mice (AEG-1ΔHEP and AEG-1ΔMAC, respectively) and induced HCC by treatment with N-nitrosodiethylamine (DEN) and phenobarbital (PB). AEG-1ΔHEP mice exhibited a significant reduction in disease severity compared with control littermates, while AEG-1ΔMAC mice were profoundly resistant. In vitro, AEG-1-/- hepatocytes exhibited increased sensitivity to stress and senescence. Notably, AEG-1-/- macrophages were resistant to either M1 or M2 differentiation with significant inhibition in migration, endothelial adhesion, and efferocytosis activity, indicating that AEG-1 ablation renders macrophages functionally anergic. These results unravel a central role of AEG-1 in regulating macrophage activation and indicate that AEG-1 is required in both tumor cells and tumor microenvironment to stimulate hepatocarcinogenesis.Significance: These findings distinguish a novel role of macrophage-derived oncogene AEG-1 from hepatocellular AEG-1 in promoting inflammation and driving tumorigenesis. Cancer Res; 78(22); 6436-46. ©2018 AACR.

Mechanical Bridge to Transplantation with the Vienna Heart in TAH and LVAD Configuration

The Vienna heart uses a vacuum formed, pellethane pulsatile ventricle and is available in left ventricular assist (LVAD) and total artificial heart (TAH) configurations. This device was used as mechanical support of the failing heart in nine patients intended for heart transplantation. In two patients with cardiomyopathy an orthotopic TAH was implanted; one survived despite severe preoperative ischemic liver damage, and the other died of sepsis.

In seven patients an atrio-aortic LVAD was implanted; six had suffered an acute myocardial infarction with cardiogenic shock, and one could not be weaned off bypass. Three patients survived. These included one 65-year-old with incipient ARDS at operation, and a 40-year-old with preoperative liver and kidney insufficiency who was transplanted in septicemia. In this patient the septic focus, natural and artificial heart, were removed at transplantation.

Four patients died. In one we were unable to establish satisfactory circulation, one died after failure of the transplanted heart, one suffered a lethal cerebral embolism and one developed multi-organ failure after repeated attacks of ventricular fibrillation.

With the Vienna heart sufficient circulatory support could be established with cardiac outputs between 6 and 8 l/min for the TAH and 3.5 to 4.5 I/min for the LVAD. With this type of support an overall survival rate of 44% could be achieved. Mechanical hemolysis was not a clinical problem and no device failure occurred.

The Effect of Oxygen Transport Resistances on the Viability and Functions of Isolated Rat Hepatocytes

The treatment of fulminant hepatic failure with a bioartificial liver support device relies on the possibility of replacing the detoxification and synthetic functions of the injured liver for as long as needed for patient recovery. In spite of progress in cell culture techniques, the effective use of isolated hepatocytes in liver support devices is currently hampered by a lack of information on the metabolic factors limiting long term hepatocyte culture. In this paper, we report our investigation on the effects of oxygen transport resistances on the viability and functions of isolated rat hepatocytes cultured on collagen coated Petri dishes. Detoxification and synthetic functions of the hepatocytes were studied with respect to ammonia and phenolsulphonphthalein elimination and urea synthesis. Lower resistances to oxygen transport favored hepatocyte survival. The isolated hepatocytes synthesized urea at rates that decreased as the resistance to oxygen transport increased. The rate at which urea was synthesized also decreased during the culture. Neither PSP, nor ammonia elimination rate was greatly affected by increasing oxygen transport resistances and remained rather constant up to a week of culture.

Cell biology is different in small volumes: endogenous signals shape phenotype of primary hepatocytes cultured in microfluidic channels

The approaches for maintaining hepatocytes in vitro are aimed at recapitulating aspects of the native liver microenvironment through the use of co-cultures, surface coatings and 3D spheroids. This study highlights the effects of spatial confinement-a less studied component of the in vivo microenvironment. We demonstrate that hepatocytes cultured in low-volume microfluidic channels (microchambers) retain differentiated hepatic phenotype for 21 days whereas cells cultured in regular culture plates under identical conditions de-differentiate after 7 days. Careful consideration of nutrient delivery and oxygen tension suggested that these factors could not solely account for enhanced cell function in microchambers. Through a series of experiments involving microfluidic chambers of various heights and inhibition of key molecular pathways, we confirmed that phenotype of hepatocytes in small volumes was shaped by endogenous signals, both hepato-inductive growth factors (GFs) such as hepatocyte growth factor (HGF) and hepato-disruptive GFs such as transforming growth factor (TGF)-β1. Hepatocytes are not generally thought of as significant producers of GFs–this role is typically assigned to nonparenchymal cells of the liver. Our study demonstrates that, in an appropriate microenvironment, hepatocytes produce hepato-inductive and pro-fibrogenic signals at the levels sufficient to shape their phenotype and function.

Novel FXR (farnesoid X receptor) modulators: Potential therapies for cholesterol gallstone disease

Metabolic disorders such as diabetes are known risk factors for developing cholesterol gallstone disease (CGD). Cholesterol gallstone disease is one of the most prevalent digestive diseases, leading to considerable financial and social burden worldwide. Ursodeoxycholic acid (UDCA) is the only bile acid drug approved by FDA for the non-surgical treatment of gallstones. However, the molecular link between UDCA and CGD is unclear. Previous data suggest that the farnesoid X receptor (FXR), a bile acid nuclear receptor, may protect against the development of CGD. In studies aimed at identifying the role of FXR, we recently identify a novel chemical tool, 6EUDCA (6-αethyl-ursodeoxycholic acid), a synthetic derivative of UDCA, for studying FXR. We found that 6EUDCA binds FXR stronger than UDCA in a TR-FRET binding assay. This result was supported by computational docking models that suggest 6EUDCA forms a more extensive hydrogen bound network with FXR. Interestingly, neither compound could activate FXR target genes in human nor mouse liver cells, suggesting UDCA and 6EUDCA activate non-genomic signals in an FXR-dependent manner. Overall these studies may lead to the identification of a novel mechanism by which bile acids regulate cell function, and 6EUDCA may be an effective targeted CGD therapeutic.

Models and methods for in vitro testing of hepatic gap junctional communication

Inherent to their pivotal roles in controlling all aspects of the liver cell life cycle, hepatocellular gap junctions are frequently disrupted upon impairment of the homeostatic balance, as occurs during liver toxicity. Hepatic gap junctions, which are mainly built up by connexin32, are specifically targeted by tumor promoters and epigenetic carcinogens. This renders inhibition of gap junction functionality a suitable indicator for the in vitro detection of nongenotoxic hepatocarcinogenicity. The establishment of a reliable liver gap junction inhibition assay for routine in vitro testing purposes requires a cellular system in which gap junctions are expressed at an in vivo-like level as well as an appropriate technique to probe gap junction activity. Both these models and methods are discussed in the current paper, thereby focusing on connexin32-based gap junctions.

Hepatocytes maintain greater fluorescent bile acid accumulation and greater sensitivity to drug-induced cell death in three-dimensional matrix culture

Primary hepatocytes undergo phenotypic dedifferentiation upon isolation from liver that typically includes down regulation of uptake transporters and up regulation of efflux transporters. Culturing cells between layers of collagen in a three‐dimensional (3D) “sandwich” is reported to restore hepatic phenotype. This report examines how 3D culturing affects accumulation of fluorophores, the cytotoxic response to bile acids and drugs, and whether cell to cell differences in fluorescent anion accumulation correlate with differences in cytotoxicity. Hepatocytes were found to accumulate fluorescent bile acid (FBA) at significantly higher levels than the related fluorophores, carboxyfluorescein diacetate, (4.4‐fold), carboxyfluorescein succinimidyl ester (4.8‐fold), and fluorescein (30‐fold). In 2D culture, FBA accumulation decreased to background levels by 32 h, Hoechst nuclear accumulation strongly decreased, and nuclear diameter increased, indicative of an efflux phenotype. In 3D culture, FBA accumulation was maintained through 168 h but at 1/3 the original intensity. Cell to cell differences in accumulated FBA did not correlate with levels of liver zonal markers L‐FBAP (zone 1) or glutamine synthetase (zone 3). Cytotoxic response to hydrophobic bile acids, acetaminophen, and phalloidin was maintained in 3D culture, and cells with higher FBA accumulation showed 12–18% higher toxicity than the total population toward hydrophobic bile acids (P < 0.05). Long‐term imaging showed oscillations in the accumulation of FBA over periods of hours. Overall, the studies suggest that high accumulation of FBA can indicate the sensitivity of cultured hepatocytes to hydrophobic bile acids and other toxins.

These studies use automated image analysis and fluorescent dye accumulation to demonstrate that 3D culturing enhances organic anion accumulation and cytotoxic response in long‐term hepatocyte cultures. The level of anion accumulation was found to vary through days in culture and also between single cells, and higher fluorescent bile acid accumulation correlated with higher toxic response to hydrophobic bile acids.

The impact of solute carrier (SLC) drug uptake transporter loss in human and rat cryopreserved hepatocytes on clearance predictions

Cryopreserved hepatocytes are often used as a convenient tool in studies of hepatic drug metabolism and disposition. In this study, the expression and activity of drug transporters in human and rat fresh and cryopreserved hepatocytes was investigated. In human cryopreserved hepatocytes, Western blot analysis indicated that protein expression of the drug uptake transporters [human Na(+)-taurocholate cotransporting polypeptide (NTCP), human organic anion transporting polypeptides (OATPs), human organic anion transporters, and human organic cation transporters (OCTs)] was considerably reduced compared with liver tissue. In rat cryopreserved cells, the same trend was observed but to a lesser extent. Several rat transporters were reduced as a result of both isolation and cryopreservation procedures. Immunofluorescence showed that a large portion of remaining human OATP1B1 and OATP1B3 transporters were internalized in human cryopreserved hepatocytes. Measuring uptake activity using known substrates of OATPs, OCTs, and NTCP showed decreased activity in cryopreserved as compared with fresh hepatocytes in both species. The reduced uptake in cryopreserved hepatocytes limited the in vitro metabolism of several AstraZeneca compounds. A retrospective analysis of clearance predictions of AstraZeneca compounds suggested systematic lower clearance predicted using metabolic stability data from human cryopreserved hepatocytes compared with human liver microsomes. This observation is consistent with a loss of drug uptake transporters in cryopreserved hepatocytes. In contrast, the predicted metabolic clearance from fresh rat hepatocytes was consistently higher than those predicted from liver microsomes, consistent with retention of uptake transporters. The uptake transporters, which are decreased in cryopreserved hepatocytes, may be rate-limiting for the metabolism of the compounds and thus be one explanation for underpredictions of in vivo metabolic clearance from cryopreserved hepatocytes.

Functional ATP-binding cassette drug efflux transporters in isolated human and rat hepatocytes significantly affect assessment of drug disposition

Freshly isolated hepatocytes are considered the gold standard for in vitro studies of hepatic drug disposition. To ensure a reliable supply of cells, cryopreserved human hepatocytes are often used. ABC-superfamily drug efflux transporters are key elements in hepatic drug disposition. These transporters are often considered lost after isolation of hepatocytes. In the present study, the expression and activity of ABC transporters BCRP, BSEP, P-gp, MRP2, MRP3, and MRP4 in human and rat cryopreserved hepatocytes were investigated. In commercially available human cryopreserved hepatocytes, all drug efflux transporters except human BCRP (hBCRP) exhibited similar expression levels as in fresh liver biopsies. Expression levels of hBCRP were 60% lower in cryopreserved human hepatocytes than in liver tissue, which could lead to, at most, a 2.5-fold reduction in hBCRP-mediated efflux. Fresh rat hepatocytes showed significantly lower levels of rat BCRP compared with liver expression levels; expression levels of other ABC transporters were unchanged. ABC transporters in human cryopreserved cells were localized to the plasma membrane. Functional studies could demonstrate P-gp and BCRP activity in both human cryopreserved and fresh rat hepatocytes. Inhibiting P-gp-mediated efflux by elacridar in in vitro experiments significantly decreased fexofenadine efflux from hepatocytes, resulting in an increase in apparent fexofenadine uptake. The results from the present study clearly indicate that ABC transporter-mediated efflux in freshly isolated as well as cryopreserved rat and human hepatocytes should be taken into account in in vitro experiments used for modeling of drug metabolism and disposition.

Development of novel dual binders as potent, selective, and orally bioavailable tankyrase inhibitors

Tankyrases (TNKS1 and TNKS2) are proteins in the poly ADP-ribose polymerase (PARP) family. They have been shown to directly bind to axin proteins, which negatively regulate the Wnt pathway by promoting β-catenin degradation. Inhibition of tankyrases may offer a novel approach to the treatment of APC-mutant colorectal cancer. Hit compound 8 was identified as an inhibitor of tankyrases through a combination of substructure searching of the Amgen compound collection based on a minimal binding pharmacophore hypothesis and high-throughput screening. Herein we report the structure- and property-based optimization of compound 8 leading to the identification of more potent and selective tankyrase inhibitors 22 and 49 with improved pharmacokinetic properties in rodents, which are well suited as tool compounds for further in vivo validation studies.

The effects of human umbilical cord perivascular cells on rat hepatocyte structure and functional polarity

Hepatocyte culture is a useful tool for the study of their biology and the development of bioartificial livers. However, many challenges have to be overcome since hepatocytes rapidly lose their normal phenotype in vitro. We have recently demonstrated that human umbilical cord perivascular cells (HUCPVCs) are able to provide support to hepatocytes. In the present study we go further into exploring the effects that HUCPVCs have in the functional polarization, and both the internal and external organization, of hepatocytes. Also, we investigate HUCPVC–hepatocyte crosstalk by tracking both the effects of HUCPVCs on hepatocyte transcription factors and those of hepatocytes on the expression of hepatotrophic factors in HUCPVCs. Our results show that HUCPVCs maintain the functional polarity of hepatocytes ex vivo, as judged by the secretion of fluorescein into bile canaliculi, for at least 40 days. Transmission electron microscopy revealed that hepatocytes in coculture organize in an organoid-like structure embedded in extracellular matrix surrounded by HUCPVCs. In coculture, hepatocytes displayed a higher expression of C/EBPα, implicated in maintenance of the mature hepatocyte phenotype, and HUCPVCs upregulated hepatocyte growth factor and Jagged1 indicating that these genes may play important roles in HUCPVC–hepatocyte interactions.

Metabolism and disposition of acetaminophen: recent advances in relation to hepatotoxicity and diagnosis

Acetaminophen (APAP) is one of the most widely used drugs. Though safe at therapeutic doses, overdose causes mitochondrial dysfunction and centrilobular necrosis in the liver. The first studies of APAP metabolism and activation were published more than 40 years ago. Most of the drug is eliminated by glucuronidation and sulfation. These reactions are catalyzed by UDP-glucuronosyltransferases (UGT1A1 and 1A6) and sulfotransferases (SULT1A1, 1A3/4, and 1E1), respectively. However, some is converted by CYP2E1 and other cytochrome P450 enzymes to a reactive intermediate that can bind to sulfhydryl groups. The metabolite can deplete liver glutathione (GSH) and modify cellular proteins. GSH binding occurs spontaneously, but may also involve GSH-S-transferases. Protein binding leads to oxidative stress and mitochondrial damage. The glucuronide, sulfate, and GSH conjugates are excreted by transporters in the canalicular (Mrp2 and Bcrp) and basolateral (Mrp3 and Mrp4) hepatocyte membranes. Conditions that interfere with metabolism and metabolic activation can alter the hepatotoxicity of the drug. Recent data providing novel insights into these processes, particularly in humans, are reviewed in the context of earlier work, and the effects of altered metabolism and reactive metabolite formation are discussed. Recent advances in the diagnostic use of serum adducts are covered.

The volume of distribution is an indicator of poor in vitro-in vivo extrapolation of clearance for acidic drugs in the rat

Abstract 1. We applied the regression offset approach to predict rat in vivo intrinsic clearance (CLint) for 54 new chemical acid entities with high plasma protein binding values and low renal clearance (CL). The prediction success was correlated to volume of distribution (Vd), molecular weight (Mw) and CL. 2. A correlation between poor in vitro-in vivo extrapolation (IVIVE) and Vd values distinct from the Vd of albumin (0.1-0.2 L/kg) was revealed. For compounds with a Vd value above 0.5 L/kg, 0% of the predictions of in vivo CLint was within twofold of the observed value, compared to 69% for compounds with a Vd value below 0.5 L/kg. 3.  Compounds with a Mw below 450 g/mol demonstrated more accurate in vivo CLint predictions than compounds with a Mw above 450 g/mol, i.e. 63% compared to 21% within twofold. For compounds with in vivo CL below 30% of the liver blood flow (LBF), 53% of the predictions was within twofold of the observed value, compared to 0% for compounds with CL above 30% of the LBF. 4. We show that accurate IVIVE for acidic compounds with high plasma protein binding and low renal CL can be associated with a low Vd (i.e. around the Vd of albumin) and with a low in vivo CL, and that Mw is an important optimization parameter for pharmacokinetic. This study also further demonstrates the advantages of the application of the regression method for identifying cases when metabolic CL is not the single major elimination pathway.

Label-free evaluation of hepatic microvesicular steatosis with multimodal coherent anti-Stokes Raman scattering microscopy

Hepatic microvesicular steatosis is a hallmark of drug-induced hepatotoxicity and early-stage fatty liver disease. Current histopathology techniques are inadequate for the clinical evaluation of hepatic microvesicular steatosis. In this paper, we explore the use of multimodal coherent anti-Stokes Raman scattering (CARS) microscopy for the detection and characterization of hepatic microvesicular steatosis. We show that CARS microscopy is more sensitive than Oil Red O histology for the detection of microvesicular steatosis. Computer-assisted analysis of liver lipid level based on CARS signal intensity is consistent with triglyceride measurement using a standard biochemical assay. Most importantly, in a single measurement procedure on unprocessed and unstained liver tissues, multimodal CARS imaging provides a wealth of critical information including the detection of microvesicular steatosis and quantitation of liver lipid content, number and size of lipid droplets, and lipid unsaturation and packing order of lipid droplets. Such information can only be assessed by multiple different methods on processed and stained liver tissues or tissue extracts using current standard analytical techniques. Multimodal CARS microscopy also permits label-free identification of lipid-rich non-parenchymal cells. In addition, label-free and non-perturbative CARS imaging allow rapid screening of mitochondrial toxins-induced microvesicular steatosis in primary hepatocyte cultures. With its sensitivity and versatility, multimodal CARS microscopy should be a powerful tool for the clinical evaluation of hepatic microvesicular steatosis.

In vitro expansion and functional recovery of mature hepatocytes from mouse adult liver

BACKGROUND

Mature hepatocytes retain the ability to regenerate the liver lobule fully in vivo following injury. Several cytokines and soluble factors (hepatocyte growth factors, epidermal growth factors, insulin and nicotinamide) are known to be important for proliferation of mature hepatocytes in vitro. However, hepatocytes monolayer-cultured on extracellular matrices have gradually lost their specific functions, particularly those in drug metabolism.

AIM

We have explored and established a new culture system for expansion of functional hepatocytes.

METHODS

We evaluated two approaches for efficient expansion of mature hepatocytes: (i) Co-culture with mouse embryonic fibroblasts (MEF); (ii) Addition to culture of inhibitors of cell signals involved in liver regeneration. After expansion steps, 3-dimensional spheroid-forming culture was used to re-induce mature hepatocellular function.

RESULTS

The addition of inhibitors for tumour growth factor (TGF) β and glycogen synthase kinase (GSK) 3β efficiently induced in vitro expansion of mature hepatocytes. Although expression of hepatocellular functional genes decreased after expansion in monolayer culture, their expression and the activity of cytochrome P450 enzymes significantly increased with spheroid formation. Furthermore, when hepatocytes were co-cultured with MEF, addition of a MAPK/ERK kinase (MEK) inhibitor at the spheroid formation step enhanced drug-metabolism-related gene expression.

CONCLUSION

Combination of the MEF co-culture system with the addition of inhibitors of TGFβ and GSK3β induced in vitro expansion of hepatocytes. Moreover, expression of mature hepatocellular genes and the activity of drug-metabolism enzymes in expanded hepatocytes were re-induced after spheroid culture.

Bile acids regulate hepatic gluconeogenic genes and farnesoid X receptor via G(alpha)i-protein-coupled receptors and the AKT pathway

Bile acids are important regulatory molecules that can activate specific nuclear receptors and cell signaling pathways in the liver and gastrointestinal tract. In the current study, the chronic bile fistula (CBF) rat model and primary rat hepatocytes (PRH) were used to study the regulation of gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase) and the gene encoding short heterodimeric partner (SHP) by taurocholate (TCA). The intestinal infusion of TCA into the CBF rat rapidly (1h) activated the AKT (approximately 9-fold) and ERK1/2 (3- to 5-fold) signaling pathways, downregulated (approximately 50%, 30 min) the mRNA levels of PEPCK and G-6-Pase, and induced (14-fold in 3 h) SHP mRNA. TCA rapidly ( approximately 50%, 1-2 h) downregulated PEPCK and G-6-Pase mRNA levels in PRH. The downregulation of these genes by TCA was blocked by pretreatment of PRH with pertussis toxin (PTX). In PRH, TCA plus insulin showed a significantly stronger inhibition of glucose secretion/synthesis from lactate and pyruvate than either alone. The induction of SHP mRNA in PRH was strongly blocked by inhibition of PI3 kinase or PKCzeta by specific chemical inhibitors or knockdown of PKCzeta by siRNA encoded by a recombinant lentivirus. Activation of the insulin signaling pathway appears to be linked to the upregulation of farnesoid X receptor functional activity and SHP induction.

Transcription factor Late SV40 Factor (LSF) functions as an oncogene in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly aggressive cancer with no currently available effective treatment. Understanding of the molecular mechanism of HCC development and progression is imperative for developing novel, effective, and targeted therapies for this lethal disease. In this article, we document that the cellular transcription factor Late SV40 Factor (LSF) plays an important role in HCC pathogenesis. LSF protein was significantly overexpressed in human HCC cells compared to normal hepatocytes. In 109 HCC patients, LSF protein was overexpressed in >90% cases, compared to normal liver, and LSF expression level showed significant correlation with the stages and grades of the disease. Forced overexpression of LSF in less aggressive HCC cells resulted in highly aggressive, angiogenic, and multiorgan metastatic tumors in nude mice. Conversely, inhibition of LSF significantly abrogated growth and metastasis of highly aggressive HCC cells in nude mice. Microarray studies revealed that as a transcription factor, LSF modulated specific genes regulating invasion, angiogenesis, chemoresistance, and senescence. The expression of osteopontin (OPN), a gene regulating every step in tumor progression and metastasis, was robustly up-regulated by LSF. It was documented that LSF transcriptionally up-regulates OPN, and loss-of-function studies demonstrated that OPN plays an important role in mediating the oncogenic functions of LSF. Together, these data establish a regulatory role of LSF in cancer, particularly HCC pathogenesis, and validate LSF as a viable target for therapeutic intervention.

Contribution of bone marrow mesenchymal stem cells to porcine hepatocyte culture in vitro

One of the greatest challenges in the attempt to create functional bioartificial liver designs is the maintenance of porcine hepatocyte differentiated functions in vitro. Co-cultivation of hepatocytes with nonparenchymal cells may be beneficial for optimizing cell functions via mimicry of physiological microenvironment. However, the underlying mechanisms remain to be elucidated. An equal number of freshly isolated porcine hepatocytes and purified bone marrow mesenchymal stem cells (MSCS) was randomly co-cultured and the morphological and functional changes of heterotypic interactions were characterized. Furthermore, contributions of soluble factors involved in the separated co-culture system were evaluated. The purity of the third-passage MSCS and primary hepatocytes was more than 90% and 99%, respectively. Hepatocyte viability was greater than 95%. A rapid attachment and self-organization of three-dimensional hepatocyte spheroids were encouraged, which was due to the supporting MSCS of high motility. The elevated induction of both albumin production and urea synthesis was achieved in co-culture (P < 0.05). Data from semipermeable membrane cultures suggested that interleukin-6 is one of the key stimulators in hepatic functional enhancement. These results demonstrate for the first time that soluble factors have beneficial effects on the preservation of hepatic morphology and functionality in the co-culture of hepatocytes with MSCS in vitro, which could represent a promising tool for tissue engineering, cell biology, and bioartificial liver devices.

Thyroid hormone is necessary for expression of constitutive androstane receptor in rat hepatocytes

Small hepatocytes are hepatocyte progenitor cells that possess the capability of maturation and cryopreservation. When cryopreserved rat small hepatocytes were cultured in serum-free medium, the protein expression and the inducibility of CYP1A1/2, CYP2E1, and CYP3A were maintained, but those of CYP2B1 were lost. In this study we investigated the cause of the loss of CYP2B1 expression in cryopreserved small hepatocytes by reverse transcription-polymerase chain reaction, immunoblotting, and chromatin immunoprecipitation assay. Expression of mRNA and protein of the nuclear receptor, constitutive androstane receptor (CAR), which regulates the expression of CYP2B1, was inhibited in the serum-free culture of cryopreserved small hepatocytes, whereas they were expressed in that of subcultured small hepatocytes. Serum application dramatically induced CAR expression in the culture of cryopreserved small hepatocytes. The addition of very low concentrations of thyroid hormones (THs; 3,5,3'-triiodothyronine, 5 x 10(-12) M; thyroxine, 5 x 10(-12)-5 x 10(-10) M) to the medium also induced the expression of CAR and CYP2B1. Moreover, CYP2B1 expression was induced by administration of phenobarbital. In rats with hypothyroidism induced by thyroidectomy and 6-propyl-2-thiouracil treatment, the expression of CAR and CYP2B1 was strongly repressed. Although THs do not directly regulate the expression of CAR, they may be important for rat hepatocytes to regulate CYP2B1 through CAR expression in the physiological condition.

Astrocyte elevated gene-1 regulates hepatocellular carcinoma development and progression

Hepatocellular carcinoma (HCC) is a highly aggressive vascular cancer characterized by diverse etiology, activation of multiple signal transduction pathways, and various gene mutations. Here, we have determined a specific role for astrocyte elevated gene-1 (AEG1) in HCC pathogenesis. Expression of AEG1 was extremely low in human hepatocytes, but its levels were significantly increased in human HCC. Stable overexpression of AEG1 converted nontumorigenic human HCC cells into highly aggressive vascular tumors, and inhibition of AEG1 abrogated tumorigenesis by aggressive HCC cells in a xenograft model of nude mice. In human HCC, AEG1 overexpression was associated with elevated copy numbers. Microarray analysis revealed that AEG1 modulated the expression of genes associated with invasion, metastasis, chemoresistance, angiogenesis, and senescence. AEG1 also was found to activate Wnt/beta-catenin signaling via ERK42/44 activation and upregulated lymphoid-enhancing factor 1/T cell factor 1 (LEF1/TCF1), the ultimate executor of the Wnt pathway, important for HCC progression. Inhibition studies further demonstrated that activation of Wnt signaling played a key role in mediating AEG1 function. AEG1 also activated the NF-kappaB pathway, which may play a role in the chronic inflammatory changes preceding HCC development. These data indicate that AEG1 plays a central role in regulating diverse aspects of HCC pathogenesis. Targeted inhibition of AEG1 might lead to the shutdown of key elemental characteristics of HCC and could lead to an effective therapeutic strategy for HCC.

Heterotypic interactions in the preservation of morphology and functionality of porcine hepatocytes by bone marrow mesenchymal stem cells in vitro

Temporary replacement of specific liver functions with extracorporeal bioartificial liver has been hampered by rapid de-differentiation of porcine hepatocytes in vitro. Co-cultivation of hepatocytes with non-parenchymal cells may be beneficial for optimizing cell functions via mimicry of physiological microenvironment consisting of endogenous matrix proteins. However, the underlying mechanisms remain to be elucidated. A randomly distributed co-culture system composed of porcine hepatocytes and bone marrow mesenchymal stem cells was generated, and the morphological and functional changes of varying degrees of heterotypic interactions were characterized. Furthermore, contributions of extracellular matrix within this co-culture were evaluated. A rapid attachment and self-organization of three-dimensional hepatocyte spheroids were encouraged. Studies on hepatocyte viability showed a metabolically active, viable cell population in all co-culture configurations with occurrence of few dead cells. The maximal induction of albumin production, urea synthesis, and cytochrome P4503A1 activities was achieved at seeding ratio of 2:1. Immunocytochemical detection of various extracellular matrix confirmed that a high level of matrix proteins synthesis within distinct cells was involved in hepatocyte homeostasis. These results demonstrate for the first time that cell-matrix has synergic effects on the preservation of hepatic morphology and functionality in the co-culture of porcine hepatocytes with mesenchymal stem cells in vitro, which could represent a promising tool for tissue engineering, cell biology, and bioartificial liver devices.

PTK787/ZK22258 attenuates stellate cell activation and hepatic fibrosis in vivo by inhibiting VEGF signaling

Liver fibrosis due to hepatic stellate cell (HSC) activation represents a common response to chronic liver injury. PTK787/ZK222584 (PTK/ZK) is a pan-VEGFR tyrosine kinase inhibitor. The aim of this study was to examine the effect of PTK/ZK in liver fibrosis. In primary HSCs, PTK/ZK inhibited the expression of alpha-smooth muscle actin (alpha-SMA), collagen, tissue inhibitor of metalloproteinase-1 (TIMP-1), as well as cell proliferation, migration and actin filament formation. PTK/ZK-induced apoptosis of HSCs, which was correlated with increased caspase-3 activation and suppressed Bcl-2 expression. PTK/ZK also induced cell cycle arrest, accompanied by increasing the expression of p27(Kip1) and downregulation of cyclin D1 and cyclin E. PTK/ZK significantly inhibited vascular endothelial growth factor (VEGF) expression, as well as VEGF-simulated cell proliferation and phosphorylation of Akt in activated HSCs. In a murine fibrotic liver, PTK/ZK attenuated collagen deposition and alpha-SMA expression in carbon tetrachloride-induced fibrosis in both a 'prevention' and 'treatment' dosing scheme. These beneficial effects were associated with reduced phosphorylation of Akt and suppressed mRNA expression of procollagen-(I), TIMP-1, matrix metalloproteinase-9 and CD31. These findings provide novel insights into the potential value of blocking VEGF signaling by a small molecule tyrosine kinase inhibitor in treating hepatic fibrosis.

Impaired glutathione-conjugating capacity by cryopreserved human and rat hepatocytes

The activity of glutathione transferase was measured in sonicates of fresh rat hepatocytes and of cryopreserved rat, human and dog hepatocytes in the presence of added glutathione and by using 1-chloro-2,4-dinitrobenzene (CDNB) as non-selective substrate. The glutathione-conjugating capacity was also investigated in the presence of CDNB alone (without glutathione) with intact fresh rat hepatocytes and cryopreserved rat and human hepatocytes. Finally, the intracellular level of glutathione was measured in these hepatocytes. The specific activity of glutathione transferase in sonicates of fresh rat hepatocytes (in the presence of added GSH and CDNB) was about 415 nmol/min/10(6) cells. The corresponding activities in cryopreserved rat, human and dog hepatocytes were approximately 320, 440 and 540 nmol/min/10(6) cells, respectively. In contrast, glutathione conjugation by the intact cryopreserved human and rat hepatocytes in the presence of CDNB alone was less than 10% of the corresponding conjugation by fresh rat hepatocytes, indicating that glutathione was depleted in these cryopreserved hepatocytes. Glutathione depletion was confirmed after analytical measurement of the glutathione levels in fresh and cryopreserved hepatocytes. In fresh rat hepatocytes the level of glutathione was 44 nmol/10(6) cells, whereas it was 2.5 and 4.4 nmol/10(6) cells in cryopreserved rat and human hepatocytes, respectively. In summary, glutathione transferase was active in these cryopreserved hepatocytes but the cryopreservation procedure likely causes depletion in the intracellular level of glutathione, resulting in an overall reduced glutathione conjugating capacity.

Intracellular cholesterol transporter StarD4 binds free cholesterol and increases cholesteryl ester formation

StarD4 protein is a member of the StarD4 subfamily of steroidogenic acute regulatory-related lipid transfer (START) domain proteins that includes StarD5 and StarD6, proteins whose functions remain poorly defined. The objective of this study was to isolate and characterize StarD4's sterol binding and to determine in a hepatocyte culture model its sterol transport capabilities. Utilizing purified full-length StarD4, in vitro binding assays demonstrated a concentration-dependent binding of [(14)C]cholesterol by StarD4 similar to that of the cholesterol binding START domain proteins StarD1 and StarD5. Other tested sterols showed no detectable binding to StarD4, except for 7alpha-hydroxycholesterol, for which StarD4 demonstrated weak binding on lipid protein overlay assays. Subsequently, an isolated mouse hepatocyte model was used to study the ability of StarD4 to bind/mobilize/distribute cellular cholesterol. Increased expression of StarD4 in primary mouse hepatocytes led to a marked increase in the intracellular cholesteryl ester concentration and in the rates of bile acid synthesis. The ability and specificity of StarD4 to bind cholesterol and, as a function of its level of expression, to direct endogenous cellular cholesterol suggest that StarD4 plays an important role as a directional cholesterol transporter in the maintenance of cellular cholesterol homeostasis.

Ethanol stimulates bile acid formation in primary human hepatocytes

The conversion of cholesterol to bile acids is a key pathway for elimination of cholesterol from the body, thereby reducing the risk of arteriosclerosis. Moderate consumption of ethanol has been shown to have preventive effects on cardiovascular disease and decrease the risk of gallstone formation. In the present study primary human hepatocytes were used to investigate if ethanol affected bile acid synthesis. Hepatocytes were prepared from donor liver (n=11) and treated with ethanol, 7.7 or 50 mM, for 24 h. mRNA levels for enzymes in bile acid synthesis pathways were studied and bile acid synthesis was analyzed. Treatment with 7.7 mM ethanol increased cholic acid synthesis by 20% and treatment with 50 mM ethanol up-regulated cholic acid formation by 60%. The synthesis of cholic acid increased more than that of chenodeoxycholic acid, indicating that the classical pathway for bile acid synthesis was up-regulated. Increased bile acid levels in the cells treated with ethanol were seen after approximately 20 h. mRNA expression of CYP7A1, CYP27A1, and CYP8B1 in the hepatocytes was not affected by alcohol exposure.

In vivo regulation of p21 by the Kruppel-like factor 6 tumor-suppressor gene in mouse liver and human hepatocellular carcinoma

Kruppel-like factor (KLF) 6 is a tumor-suppressor gene functionally inactivated by loss of heterozygosity, somatic mutation and/or alternative splicing that generates a dominant-negative splice form, KLF6-SV1. Wild-type KLF6 (wtKLF6) expression is decreased in many human malignancies, which correlates with reduced patient survival. Additionally, loss of the KLF6 locus in the absence of somatic mutation in the remaining allele occurs in a number of human cancers, raising the possibility that haploinsufficiency of the KLF6 gene alone contributes to cellular growth dysregulation and tumorigenesis. Our earlier studies identified the cyclin-dependent kinase inhibitor p21 as a transcriptional target of the KLF6 gene in cultured cells, but not in vivo. To address this issue, we have generated two genetic mouse models to define the in vivo role of KLF6 in regulating cell proliferation and p21 expression. Transgenic overexpression of KLF6 in the liver resulted in a runted phenotype with decreased body and liver size, with evidence of decreased hepatocyte proliferation, increased p21 and reduced proliferating cell nuclear antigen expression. In contrast, mice with targeted deletion of one KLF6 allele (KLF6+/-) display increased liver mass with reduced p21 expression, compared to wild type littermates. Moreover, in primary hepatocellular carcinoma samples, there is a significant correlation between wtKLF6 and p21 mRNA expression. Combined, these data suggest that haploinsufficiency of the KLF6 gene may regulate cellular proliferation in vivo through decreased transcriptional activation of the cyclin-dependent kinase inhibitor p21.

Cytochrome p450 expression of cultured rat small hepatocytes after long-term cryopreservation

Small hepatocytes (SHs) are hepatic progenitor cells that can be cryopreserved for a long time. After thawing, the cells can proliferate and, when treated with Matrigel, they can differentiate into mature hepatocytes (MHs). In this study, we investigated whether cryopreserved SHs could express cytochromes P450 (P450s), whether P450 expression was induced by appropriate inducers, and whether P450 activities were measurable. 3-Methylcholanthrene (3-MC), phenobarbital (PB), pregnenolone-16alpha-carbonitrile (PCN), and ethanol were used as inducers for CYP1A, 2B, 3A, and 2E, respectively. Immunoblot analysis indicated that cryopreserved SHs constitutively expressed CYP1A1/2, CYP2E1, and CYP3A2 as much as 26 days after plating. Significant expression of CYP1A1/2 and 3A2 in the cells treated with Matrigel was induced by 3-MC and PCN, respectively. Although Matrigel did not up-regulate the enzymatic activity of CYP1A, CYP3A and CYP2E activities increased. Induction of CYP1A and CYP3A activities by each inducer was observed in cryopreserved cells treated with Matrigel. Although the expression of CYP2B1 could be detected in subcultured SHs treated with PB, it was not detected in cryopreserved SHs. The activity of NADPH-cytochrome P450 reductase was measured in both subcultured and cryopreserved SHs, although the activities in both were approximately 30% of that of MHs. Profiles of (14)C-testosterone metabolites were examined in cultured MHs and in cryopreserved SHs by high-performance liquid chromatography. Similar peaks for testosterone metabolites in MHs and SHs were observed in the same elution time. These results indicate that, although induction of CYP3A and 2B in cryopreserved SHs is inferior to that in subcultured ones, SHs can maintain the expression and activities of P450s after long-term cryopreservation.

Determination of the hepatocellularity number for human, dog, rabbit, rat and mouse livers from protein concentration measurements

Biologically based scaling factors have to be used to predict in vivo metabolic clearance of xenobiotics from data obtained in vitro. Although standard values for the hepatocellularity numbers for different species are used in the literature, detailed information on the determination of these values has only been presented for humans and rats, and somewhat different results have been obtained in different studies. The present work was undertaken in order to determine the number of hepatocytes per gram of liver for human, dog, rabbit, rat and mouse livers. Hepatocellularity numbers were calculated from the ratio between the liver protein concentration and the protein concentration in the corresponding hepatocyte suspension. For human, rabbit, rat and mouse livers, the hepatocellular values were in the same range, more precisely 139+/-25, 114+/-20, 117+/-30 and 135+/-10 million cells per gram of liver, respectively. However, for the dog liver, the corresponding value was as high as 215+/-45 million cells per gram. These values should be of importance during the scaling process of intrinsic clearance for xenobiotics in hepatocytes to in vivo hepatic clearance.

Hepatocyte spheroid formation on a titanium dioxide gel surface and hepatocyte long-term culture

The cell morphology and expression of differentiated functions of primary rat hepatocytes on a titanium dioxide (TiO(2)) gel surface were investigated. Polystyrene culture dishes were coated with TiO(2) gel by spin-coating an ethanol solution of titanium n-butoxide, hydrolyzing in a humidity chamber and drying with nitrogen gas. The TiO(2) gel layer formed on the polystyrene dishes was transparent and robust, and its surface was quite flat. Rat hepatocytes inoculated on the TiO(2) gel-coated polystyrene dishes gradually accumulated with increasing culture time, and then spontaneously formed many hepatocyte spheroids at 90 +/- 21 microm diameter from about 3 days of culture. The diameter of the spheroids increased during the culture, and was 151 +/- 43 microm at 14 days of culture. Ammonia removal and albumin secretion by hepatocytes on the TiO(2) gel-coated polystyrene dishes were maintained at a high level for at least 14 days of culture compared with on a type I collagen-coated dish and a non-coated polystyrene dish. These results indicate that TiO(2) gel is an adequate material for hepatocyte spheroid formation and long-term culture of spheroids.

Influence of Matrigel-overlay on constitutive and inducible expression of nine genes encoding drug-metabolizing enzymes in primary human hepatocytes

1. Previous studies reported that rat hepatocytes overlaid with extracellular matrix components (Matrigel) maintain the expression and responsiveness of drug-metabolizing enzymes. However, whether Matrigel provides similar advantages in human hepatocytes remains largely uncertain.2. The influence of Matrigel-overlay on the constitutive and phenobarbital- and oltipraz-inducible expression of nine biotransformation enzymes, cytochrome P450s 1A1, 1A2, 2B6, 3A4, and glutathione S-transferases A1, A2, M1, T1, P1, in primary human hepatocytes was evaluated.3. Hepatocytes from five livers were maintained on a rigid collagen substratum with or without Matrigel overlay and treated for 48?h with two doses of each inducer. Quantitative RT-PCR, and for selected genes, immunoblot and enzyme activity analyses, demonstrated that human hepatocytes overlaid with Matrigel showed consistently higher constitutive and inducible expression of biotransformation genes. 4. Phenobarbital-mediated responsiveness of cytochrome P450 2B6, a potential indicator of hepatocyte differentiation status, was markedly higher in overlaid relative to non-overlaid hepatocytes. 5. It is concluded that an Matrigel overlay facilitates the maintenance and induction of xenobiotic metabolizing enzymes in primary cultures of human hepatocytes.

Human StarD5, a cytosolic StAR-related lipid binding protein

Recently identified StarD5 belongs to the StarD4 subfamily, a subfamily of steroidogenic acute regulatory related lipid transfer (START) domain proteins that includes StarD4 and StarD6, proteins whose functions remain unknown. The objective of this study was to confirm StarD5's protein localization and sterol binding capabilities as measures to pursue function. Using rabbit polyclonal antibody against newly purified human histidine-tagged/StarD5 protein, StarD5 was detected in human liver. In parallel studies, increased expression of StarD5 in primary hepatocytes led to a marked increase in microsomal free cholesterol. Cell fractionation studies demonstrated StarD5 protein in liver cytosolic fractions only, suggesting StarD5 as a directional cytosolic sterol carrier. Supportive in vitro binding assays demonstrated a concentration-dependent binding of cholesterol by StarD5 similar to that of the cholesterol binding START domain protein StarD1. In contrast to selective cholesterol binding by StarD1, StarD5 bound the potent regulatory oxysterol, 25-hydroxycholesterol, in a concentration-dependent manner. StarD5 binding appeared selective for cholesterol and 25-hydroxycholesterol, as no binding was observed for other tested sterols. The ability of StarD5 to bind not only cholesterol but also 25-hydroxycholesterol, a potent inflammatory mediator and regulatory oxysterol, raises basic fundamental questions about StarD5's role in the maintenance of cellular cholesterol homeostasis.

Use of a cocktail of probe substrates for drug-metabolizing enzymes for the assessment of the metabolic capacity of hepatocyte preparations

A cocktail of the following probe substrates for human drug-metabolizing enzymes was used to characterize hepatocyte preparations: phenacetin (for CYP1A2), diclofenac (CYP2C9), diazepam (CYP2C19), bufuralol (CYP2D6), midazolam (CYP3A4/5) and 7-hydroxycoumarin (for glucuronidation and sulphation). The cocktail was incubated with cryopreserved human, dog or minipig hepatocytes or with freshly prepared rat hepatocytes. Sample analysis was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) in an Open Access environment that allowed less experienced MS operators to login, submit and analyse sample sets using predefined settings without the immediate attendance of an experienced analyst. Intrinsic clearances (CLint) were calculated from the disappearance of the compounds from the incubations. Initially, the cocktail used for human, rat and dog hepatocyte incubations contained 7-ethoxycoumarin instead of 7-hydroxycoumarin. However, 7-ethoxycoumarin had an inhibitory effect on the metabolism of phenacetin. The highest CLint estimated with human and dog hepatocytes was observed for 7-hydroxycoumarin. For rat and minipig hepatocytes, the highest CLint was observed for bufuralol. In incubations with dog and minipig hepatocytes, the lowest CLint was seen with diclofenac, whereas for human and rat hepatocytes, the lowest value was observed with diazepam and phenacetin, respectively. When the cocktail was incubated together with human hepatocytes and 1 microM ketoconazole, the CLint of midazolam was decreased to about 7.5% of the control value, whereas the metabolism of the other cocktail compounds was virtually unaffected by this CYP3A inhibitor. It is suggested that a cocktail of specific human probe substrates for drug-metabolizing enzymes can be used routinely for the determination of the metabolic capacity of hepatocyte preparations in order to ensure the quality and reproducibility of experiments. Moreover, a cocktail of specific probe substrates can also be a useful tool for studies on enzyme inhibition.

Expression of cytochrome P450 enzymes in hepatic organoid reconstructed by rat small hepatocytes

BACKGROUND AND AIMS

Small hepatocytes (SH), which are hepatic progenitor cells, were isolated from an adult rat liver. SH in a colony sometimes change their shape from small to large and from flat to rising/piled-up. The morphological changes of SH may be correlated with hepatic maturation. Cytochrome P450s (CYP) are drug-metabolizing enzymes and the expression is one of hepatic differentiated functions. However, it is well known that the re-expression and maintenance of CYP activity are very difficult in cultured hepatocytes. We investigated the expression of CYP and the enzymatic activities in long-term cultured SH.

METHODS

SH were isolated from adult rat livers and SH colonies were collected, replated on new dishes, and then cultured. CYP1A1/2, CYP2B1, CYP3A2, CYP4A1, and CYP2E1 were induced by the addition of 3-methylcholanthrene, phenobarbital, pregnenolone-16alpha-carbonitrile, clofibric acid, and ethanol, respectively. Immunocytochemistry, immunoblots, and enzyme activities were examined.

RESULTS

SH could differentiate into mature hepatocytes by the addition of Matrigel and re-express constitutive CYPs. The expression of CYP1A1/2, CYP2B1, CYP3A2, and CYP4A1 dose-dependently increased and the amounts gradually increased with time in culture, especially in the cells treated with Matrigel. Activities of CYP1A, CYP2B, CYP3A and CYP2E in SH treated with Matrigel induced by each of the inducers were approximately 120-fold, 2.8-fold, 6.4-fold and 0.8-fold higher than in the control.

CONCLUSION

The matured SH could re-express the constitutive CYP and recover inducibility, not only of protein expression but also of enzyme activities.

Steatotic liver allografts up-regulate UCP-2 expression and suffer necrosis in rats

BACKGROUND

Fatty split-liver and living-related liver transplantation is associated with massive hepatocellular necrosis during acute rejection. Uncoupling protein (UCP)-2 is a potential regulator of energy expenditure and ATP production. We investigated the role of UCP-2 and the effects of a metalloprotease inhibitor, Y-39083, on hepatocellular injury in fatty liver allografts in rats.

MATERIALS AND METHODS

Rats were treated for 6 weeks with high-ethanol or isocalic dextrose-containing liquid diets that caused characteristic pericentral lipid accumulation. Alcoholic or nonalcoholic fatty livers from ACI (RT1a) rats were transplanted into LEW (RT1l) rats orthotopically. Hepatic necrosis was determined histologically following liver transplantation. UCP-2 mRNA levels in the hepatic allograft and in primary cultured hepatocytes from fatty liver stimulated by tumor necrosis factor (TNF)-alpha were determined. Y-39083 was administered to recipient rats continuously at 5 mg/kg/day using an osmotic infusion mini-pump.

RESULTS

The acute rejection index on day 5 posttransplant in alcoholic and nonalcoholic fatty donor livers was higher than in lean grafts. Massive hepatocyte necrosis was more prominent in alcoholic than nonalcoholic fatty liver allografts and was not seen in lean allografts. UCP-2 transcripts in both alcoholic and nonalcoholic fatty liver allografts were higher than in lean allografts. Serum TNF-alpha concentrations in recipient rats with either fatty liver allograft were greater than in animals with lean allografts. In vitro UCP-2 mRNA levels in primary cultured hepatocytes from both alcoholic and nonalcoholic fatty livers increased more after stimulation with TNF-alpha than those from lean livers. In vitro TNF-alpha production by Kupffer cells isolated from alcohol-induced fatty liver allografts on day 3 posttransplant was greater than those from lean allografts. Y-39083 significantly reduced serum concentrations of TNF-alpha and prevented massive hepatocellular necrosis in rats with both alcoholic and nonalcoholic fatty liver allografts.

CONCLUSION

Liver grafts with steatosis up-regulated UCP-2. TNF-alpha further enhanced UCP-2 transcripts, inducing massive hepatocellular necrosis during acute rejection. Posttransplantation necrosis may be prevented by metalloprotease inhibitors.

Toxicity of low dose azathioprine and 6-mercaptopurine in rat hepatocytes. Roles of xanthine oxidase and mitochondrial injury

BACKGROUND/AIMS

To study effects of pharmacologic concentrations of azathioprine and 6-mercaptopurine (6-MP) on rat hepatocytes.

METHODS

Hepatocytes cultured on matrigel were incubated with azathioprine or 6-MP; effects of putative protective agents were studied. Viability (LDH leakage), reduced (GSH) and oxidized glutathione (GSSG), mitochondrial (mt) GSH, ATP and ultrastructural changes were determined.

RESULTS

Azathioprine and 6-MP (0.5-5 micromol/l) reduced viability 5-34% at day 1 and 42-92% by day 4. Allopurinol (20 microM) (xanthine oxidase inhibitor) and 2 mM Trolox (vitamin E analog) together provided near complete protection. During culture with azathioprine, GSSG increased before cell death and there was a disproportionate reduction of mtGSH and ATP, together with ultrastructural abnormalities in mitochondria. All changes were prevented by allopurinol and trolox. Discontinuation of 1 micromol/l azathioprine restored ATP levels and arrested cell injury, while culture in glucose-enriched media augmented ATP levels and ameliorated cell death.

CONCLUSIONS

Clinically relevant concentrations of azathioprine and 6-MP are toxic to rat hepatocyte cultures by a mechanism that involves oxidative stress, mitochondrial injury and ATP depletion. This can lead to irreversible de-energization and cell death by oncosis (necrosis).

Indinavir alters sterol and fatty acid homeostatic mechanisms in primary rat hepatocytes by increasing levels of activated sterol regulatory element-binding proteins and decreasing cholesterol 7α-hydroxylase mRNA levels

Human immunodeficiency virus protease inhibitors induce hyperlipidemia in many patients treated with these drugs. We examined the effects of indinavir on cholesterol and bile acid homeostatic mechanisms in a primary rat hepatocyte (PRH) culture model. In PRH, indinavir up-regulated (2.5-fold) 3-hydroxy-3-methylglutaryl-Coenzyme A reductase mRNA levels 24hr after drug addition. In these same experiments, cholesterol 7alpha-hydroxylase (CYP7A1) mRNA levels, the rate-limiting enzyme in bile acid biosynthesis, was decreased up to 10-fold. Fatty acid synthase mRNA levels were up-regulated more than 3-fold under these conditions. Indinavir did not alter CYP7A1 transcriptional activity, but decreased CYP7A1 mRNA half-life in PRH from 1.5hr to less than 0.5hr. Sterol regulatory element-binding protein-1 (SREBP-1) mature form was increased approximately 6-fold by this drug. Indinavir-induced mRNA changes and SREBP-1 mature protein levels were significantly abated by the addition of cholesterol, solubilized in beta-cyclodextrin, to culture medium. Indinavir markedly decreased endogenous cholesterol esterification and increased cholesterol in intracellular membranes in primary hepatocytes. Indinavir gavaged into intact mice also markedly increased SREBP-1 and SREBP-2 (mature forms) in hepatic nuclei. CYP7A1 mRNA was also decreased approximately 52% in indinavir-treated animals. We propose that indinavir disrupts cellular cholesterol homeostasis by increasing SREBP's and decreasing CYP7A1 mRNA.

Fas Ligand-dependent and -independent mechanisms of toxicity induced by T cell lymphomas in lymphoid organs and in the liver

In the current study, we investigated the effect of growth of FasL(+) tumors in vivo on the functions of peripheral lymphoid organs and the liver. Injection of FasL(+) LSA tumor cells into syngeneic C57BL/6 wild-type mice but not C57BL/6 lpr/lpr (Fas-deficient) mice caused apoptosis in splenocytes. Spleen cells expressing CD3, CD4, CD8, CD19, Mac-3, and CD44 were all susceptible to tumor-induced apoptosis. Also, activated T cells were more sensitive to apoptosis induced by LSA tumor cell lysate when compared to naïve T cells. In contrast, anti-Fas Abs (Jo2) induced apoptosis in only activated but not naïve T cells. When the LSA tumor-bearing mice were injected with a superantigen (SEA), these mice showed a significant decrease in the expansion of SEA-reactive Vbeta3(+) and Vbeta11(+) T cells. When injected into syngeneic mice, the FasL(+) LSA tumor cells caused hepatotoxicity, as indicated by an increase in serum aspartate aminotransferase (AST) levels. Interestingly, Fas-deficient C57BL/6 lpr/lpr mice also showed significant AST levels in the serum following LSA tumor growth. Moreover, hepatocytes isolated from C57BL/6 wild-type and C57BL/6 lpr/lpr mice were equally susceptible to apoptosis induced by LSA tumor cell lysate in vitro. Using cDNA array, LSA tumor cells were found to express several cytokine genes including IL-2, IL-7, IL-11, IL-13, IL-16, lymphotoxin beta, and tumor necrosis factor beta. Together, these data suggested that, in mice bearing FasL(+) LSA tumor, the immunotoxicity is FasL-based, whereas the hepatotoxicity, at least in part, may be FasL-independent.

Deoxycholic acid activates the c-Jun N-terminal kinase pathway via FAS receptor activation in primary hepatocytes. Role of acidic sphingomyelinase-mediated ceramide generation in FAS receptor activation

We have shown previously that bile acids can activate the JNK pathway and down-regulate cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in the neutral pathway of bile acid biosynthesis. In this study, the mechanism(s) by which deoxycholic acid (DCA) activates the JNK pathway were examined. FAS receptor (FAS-R) and acidic sphingomyelinase (ASM)-deficient hepatocytes were resistant to DCA-induced activation of the JNK pathway. Activation of the JNK pathway (2-3-fold) in response to tumor necrosis factor-alpha was similar in both wild-type and FAS-R(-/-) hepatocytes. In wild-type and FAS-R(-/-) hepatocytes, ceramide elevation was detected as early as 2 min and peaked at 10 min after DCA treatment. In contrast, ASM(-/-) hepatocytes were defective in DCA-induced ceramide generation. Treatment with DCA resulted in movement of FAS-R to the cell surface, which was blocked upon treatment with brefeldin A. However, brefeldin A failed to block DCA-mediated JNK activation in wild-type hepatocytes. DCA-induced JNK activation was independent of either the epidermal growth factor receptor activation or free radical generation. Addition of ASM to rat hepatocytes activated JNK and down-regulated CYP7A1 mRNA levels. In conclusion, these results show that DCA activates JNK and represses CYP7A1 mRNA levels in primary hepatocytes via an ASM/FAS-R-dependent mechanism that is independent of either the epidermal growth factor receptor or free radical generation.

Effects of rGH and G118RrGH on the induction of CYP2C12 and IGF-I in primary rat hepatocytes

We have investigated the induction of the CYP2C12 and IGF-I genes by rGH and a "binding site 2 mutant", G118RrGH, in primary hepatocytes derived from male and female rats. Both the basal and the induced levels of CYP2C12, but not of IGF-I, were markedly lower in male derived than in female derived hepatocytes. A lower degree of receptor occupancy appears needed to elicit the CYP2C12 than the IGF-I response in cells obtained from both gender. At 7h of GH exposure high doses of rGH caused a bell-shaped induction of IGF-1 and a plateau was reached for CYP2C12 in female derived cells. G118RrGH did not antagonize the rGH effect; in contrast G118RrGH had an agonistic effect on CYP2C12 induction in female derived cells that in dose-response experiments was bell-shaped. The difficulty in achieving bell-shaped dose-response curves with rGH, together with the lack of an antagonistic effect of G118RrGH, suggests that both binding sites of rGH have similar affinity for the rGHR. The agonistic and bell-shaped dose-related effect of G118RrGH on CYP2C12 expression indicates that G118RrGH interacts with two receptors. The results could also imply that rGH, via its site 2, can interact with other receptor molecules than rGHR.

Differential regulation of alternate UDP-glucuronosyltransferase 1A6 gene promoters by hepatic nuclear factor-1

UDP-glucuronosyltransferase 1A6 (UGT1A6) is a major UGT contributing to the glucuronidation of small phenolic compounds. The gene for rat 1A6 is expressed using two promoters, a distal promoter P1 and a proximal promoter P2. Transcripts from P2 are high in liver, gastrointestinal tract, and kidney, whereas P1 transcripts predominate in other tissues. Here we report evidence for primary control of the P2 promoter by hepatic nuclear factor 1 (HNF1). Transient transfection of a P2 reporter plasmid, p(-1354/+65) 1A6P2-luc, resulted in enhanced luciferase activity in HepG2 but not Hepa1 cells compared to cells transfected with pGL3-Basic control vector. A truncated reporter under the control of -224 to +65 exhibited comparable activity. Footprint analysis of the -224/+65 fragment revealed specific binding by rat liver nuclear protein to a region between bases -60 and -37. The binding activity was also observed with HepG2 cell but not Hepa1 cell extract. Electrophoretic mobility shift assays were consistent with the presence of HNF1 in the binding complexes. The functionality of an HNF1-binding site at -51/-37 is also supported by (1) marked decreases in the activity of P2 reporter plasmids containing a three-base substitution in the proposed HNF1 binding site and (2) the enhancement of P2 reporter activity following cotransfection of an HNF1alpha expression plasmid. The UGT1A6 P1 promoter lacks an HNF1 binding site in the analogous position and showed little response to HNF1 overexpression. Although these data do not strictly rule out an interaction between the P1 promoter and HNF1 bound to -51/-37 of P2, the results suggest a mechanism for the more abundant expression of P2-derived UGT1A6 transcripts in liver and other HNF1-enriched tissues.