A stable long-term hepatocyte culture system for studies of physiologic processes: cytokine stimulation of the acute phase response in rat and human hepatocytes

The hepatocyte proteome in organotypic rat liver models and the influence of the local microenvironment

BACKGROUND

Liver models that closely mimic the in vivo microenvironment are useful for understanding liver functions, capabilities, and intercellular communication processes. Three-dimensional (3D) liver models assembled using hepatocytes and liver sinusoidal endothelial cells (LSECs) separated by a polyelectrolyte multilayer (PEM) provide a functional system while also permitting isolation of individual cell types for proteomic analyses.

METHODS

To better understand the mechanisms and processes that underlie liver model function, hepatocytes were maintained as monolayers and 3D PEM-based formats in the presence or absence of primary LSECs. The resulting hepatocyte proteomes, the proteins in the PEM, and extracellular levels of urea, albumin and glucose after three days of culture were compared.

RESULTS

All systems were ketogenic and found to release glucose. The presence of the PEM led to increases in proteins associated with both mitochondrial and peroxisomal-based β-oxidation. The PEMs also limited production of structural and migratory proteins associated with dedifferentiation. The presence of LSECs increased levels of Phase I and Phase II biotransformation enzymes as well as several proteins associated with the endoplasmic reticulum and extracellular matrix remodeling. The proteomic analysis of the PEMs indicated that there was no significant change after three days of culture. These results are discussed in relation to liver model function.

CONCLUSIONS

Heterotypic cell-cell and cell-ECM interactions exert different effects on hepatocyte functions and phenotypes.

Pluripotent stem cell derived hepatocytes: using materials to define cellular differentiation and tissue engineering

Pluripotent stem cell derived liver cells (hepatocytes) represent a promising alternative to primary tissue for biological and clinical applications. To date, most hepatocyte maintenance and differentiation systems have relied upon the use of animal derived components. This serves as a significant barrier to large scale production and application of stem cell derived hepatocytes. Recently, the use of defined biologics has overcome those limitations in two-dimensional monolayer culture. In order to improve the cell phenotype further, three-dimensional culture systems have been employed to better mimic the in vivo situation, drawing upon materials chemistry, engineering and biology. In this review we discuss efforts in the field, to differentiate pluripotent stem cells towards hepatocytes under defined conditions.

A three-dimensional collagen-sponge-based culture system coated with simplified recombinant fibronectin improves the function of a hepatocyte cell line

Hepatocytes are widely used in pharmaceutical drug discovery tests, but their hepatic functions decrease rapidly during in vitro culture. Many culture systems have been devised to address this problem. We here report that a three-dimensional (3D) collagen-based scaffold coated with simplified recombinant fibronectin (FN) enhanced the function of a hepatocyte cell line. The developed culture system uses a honeycomb collagen sponge coated with collagen-binding domain (CBD)-cell attachment site (CAS), a chimeric protein comprising the CBD and CAS of FN. The function of HepG2 cells grown on honeycomb collagen sponge coated with CBD-CAS was investigated by determining the messenger RNA (mRNA) expression levels of several genes. The mRNA expression level of albumin increased 3.25 times in cells grown on CBD-CAS-coated honeycomb collagen sponge for 3 days; the expression level of CCAAT/enhancer binding protein (C/EBPα) increased 40-fold after 1 d and up to 150-fold after 3 d. These results suggested that CBD-CAS-coated honeycomb collagen sponge could improve the functions of hepatocytes by inducing C/EBPα expression. The activation of cytochrome P450 (CYP) enzymes in HepG2 cells grown on CBD-CAS-coated honeycomb collagen sponge was measured at the mRNA level and was found to increase between two and six times compared to cells grown without the CBD-CAS coating, showing that this culture system induced CYP gene expression and thus may be useful in drug metabolism assays.

The Use of Long-term Hepatocyte Cultures for Detecting Induction of Drug Metabolising Enzymes: The Current Status

In this report, metabolically competent in vitro systems have been reviewed, in the context of drug metabolising enzyme induction. Based on the experience of the scientists involved, a thorough survey of the literature on metabolically competent long-term culture models was performed. Following this, a prevalidation proposal for the use of the collagen gel sandwich hepatocyte culture system for drug metabolising enzyme induction was designed, focusing on the induction of the cytochrome P450 enzymes as the principal enzymes of interest. The ultimate goal of this prevalidation proposal is to provide industry and academia with a metabolically competent in vitro alternative for long-term studies. In an initial phase, the prevalidation study will be limited to the investigation of induction. However, proposals for other long-term applications of these systems should be forwarded to the European Centre for the Validation of Alternative Methods for consideration. The prevalidation proposal deals with several issues, including: a) species; b) practical prevalidation methodology; c) enzyme inducers; and d) advantages of working with independent expert laboratories. Since it is preferable to include other alternative tests for drug metabolising enzyme induction, when such tests arise, it is recommended that they meet the same level of development as for the collagen gel sandwich long-term hepatocyte system. Those tests which do so should begin the prevalidation and validation process.

Species-specific regulation of fibrinogen synthesis with implications for porcine hepatocyte xenotransplantation

BACKGROUND

Patients with liver failure could potentially be bridged with porcine xenogeneic liver cell transplantation. We examined species-specific differences between primary human and porcine hepatocytes in the regulation of coagulation protein expression and function.

METHODS

Isolated primary human and porcine hepatocytes were stimulated with either porcine or human interleukin (IL)-6 (10 ng/ml), IL-1β (10 ng/ml), and tumor necrosis factor-alpha (TNF-α, 30 ng/ml). mRNA expression of coagulation factors were measured by RT-PCR and real-time PCR. Cell culture supernatants were used for the measurement of fibrinogen by ELISA and determination of fibrin clot generation.

RESULTS

Fibrinogen expression in human hepatocytes increased after IL-6 treatment (P = 0.010) and decreased after TNF-α treatment (P = 0.005). Porcine hepatocytes displayed a lower increase in fibrinogen expression after IL-6 treatment as compared to hepatocytes of human origin (P = 0.021). Porcine hepatocytes responded contrarily following TNF-α treatment with an increased expression of fibrinogen resulting in a significant species-specific difference between human and porcine hepatocytes (P = 0.029). Fibrin polymer generation by human hepatocytes was stable and widely branched after IL-6 treatment, while stimulation with TNF-α displayed no fibrin generation at all. In contrast, treatment of porcine hepatocytes with TNF-α resulted in generation of a stable and widely branched fibrin polymer, and stimulation with IL-6 only leads to generation of partial fibrin aggregates.

CONCLUSION

We identified species-specific differences in the regulation of fibrinogen mRNA expression and fibrin generation under inflammatory stimuli. In hepatic xenotransplantation of porcine origin, these interspecies differences might lead to a loss of physiological coagulation function and a loss of transplanted cells.

Induction of albumin expression in HepG2 cells using immobilized simplified recombinant fibronectin protein

Optimization of the extracellular environment is very important for hepatocyte function in vitro. We expressed new chimeric proteins of the collagen-binding domain (CBD) with cell attachment site (CAS) of fibronectin to enhance hepatocyte function, and the CBD-CAS proteins were immobilized on collagen-coated plates. We hypothesized that the high density of CAS would increase activity of the integrin-dependent intracellular signaling pathway, thus inducing hepatocyte function. Expression of albumin in the human hepatocyte cell line HepG2 was assessed on CBD-CAS-immobilized dishes. The results indicated that the CBD-CAS-immobilized plates induced albumin expression. Immobilized CBD-CAS induced activation of focal adhesion kinase and integrin-ligand clustering on the cell membrane. These results suggest that immobilized CBD-CAS improves the function of HepG2 cells. This system could therefore be applied to drug metabolism assay in the development of new drugs.

In vitro models for liver toxicity testing

Over the years, various liver-derived in vitro model systems have been developed to enable investigation of the potential adverse effects of chemicals and drugs. Liver tissue slices, isolated microsomes, perfused liver, immortalized cell lines, and primary hepatocytes have been used extensively. Immortalized cell lines and primary isolated liver cells are currently most widely used in vitro models for liver toxicity testing. Limited throughput, loss of viability, and decreases in liver-specific functionality and gene expression are common shortcomings of these models. Recent developments in the field of in vitro hepatotoxicity include three-dimensional tissue constructs and bioartificial livers, co-cultures of various cell types with hepatocytes, and differentiation of stem cells into hepatic lineage-like cells. In an attempt to provide a more physiological environment for cultured liver cells, some of the novel cell culture systems incorporate fluid flow, micro-circulation, and other forms of organotypic microenvironments. Co-cultures aim to preserve liver-specific morphology and functionality beyond those provided by cultures of pure parenchymal cells. Stem cells, both embryonic- and adult tissue-derived, may provide a limitless supply of hepatocytes from multiple individuals to improve reproducibility and enable testing of the individual-specific toxicity. This review describes various traditional and novel in vitro liver models and provides a perspective on the challenges and opportunities afforded by each individual test system.

Dynamics of hepatic gene expression profile in a rat cecal ligation and puncture model

BACKGROUND

Sepsis remains a major clinical challenge in intensive care units. The difficulty in developing new and more effective treatments for sepsis exemplifies our incomplete understanding of the underlying pathophysiology of it. One of the more widely used rodent models for studying polymicrobial sepsis is cecal ligation and puncture (CLP). While a number of CLP studies investigated the ensuing systemic inflammatory response, they usually focus on a single time point post-CLP and therefore fail to describe the dynamics of the response. Furthermore, previous studies mostly use surgery without infection (herein referred to as sham CLP, SCLP) as a control for the CLP model, however, SCLP represents an aseptic injurious event that also stimulates a systemic inflammatory response. Thus, there is a need to better understand the dynamics and expression patterns of both injury- and sepsis-induced gene expression alterations to identify potential regulatory targets. In this direction, we characterized the response of the liver within the first 24 h in a rat model of SCLP and CLP using a time series of microarray gene expression data.

METHODS

Rats were randomly divided into three groups: sham, SCLP, and CLP. Rats in SCLP group are subjected to laparotomy, cecal ligation, and puncture while those in CLP group are subjected to the similar procedures without cecal ligation and puncture. Animals were saline resuscitated and sacrificed at defined time points (0, 2, 4, 8, 16, and 24 h). Liver tissues were explanted and analyzed for their gene expression profiles using microarray technology. Unoperated animals (Sham) serve as negative controls. After identifying differentially expressed probesets between sham and SCLP or CLP conditions over time, the concatenated data sets corresponding to these differentially expressed probesets in sham and SCLP or CLP groups were combined and analyzed using a "consensus clustering" approach. Promoters of genes that share common characteristics were extracted and compared with gene batteries comprised of co-expressed genes to identify putatative transcription factors, which could be responsible for the co-regulation of those genes.

RESULTS

The SCLP/CLP genes whose expression patterns significantly changed compared with sham over time were identified, clustered, and finally analyzed for pathway enrichment. Our results indicate that both CLP and SCLP triggered the activation of a proinflammatory response, enhanced synthesis of acute-phase proteins, increased metabolism, and tissue damage markers. Genes triggered by CLP, which can be directly linked to bacteria removal functions, were absent in SCLP injury. In addition, genes relevant to oxidative stress induced damage were unique to CLP injury, which may be due to the increased severity of CLP injury versus SCLP injury. Pathway enrichment identified pathways with similar functionality but different dynamics in the two injury models, indicating that the functions controlled by those pathways are under the influence of different transcription factors and regulatory mechanisms. Putatively identified transcription factors, notably including cAMP response element-binding (CREB), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and signal transducer and activator of transcription (STAT), were obtained through analysis of the promoter regions in the SCLP/CLP genes. Our results show that while transcription factors such as NF-κB, homeodomain transcription factor (HOMF), and GATA transcription factor (GATA) were common in both injuries for the IL-6 signaling pathway, there were many other transcription factors associated with that pathway which were unique to CLP, including forkhead (FKHD), hairy/enhancer of split family (HESF), and interferon regulatory factor family (IRFF). There were 17 transcription factors that were identified as important in at least two pathways in the CLP injury, but only seven transcription factors with that property in the SCLP injury. This also supports the hypothesis of unique regulatory modules that govern the pathways present in both the CLP and SCLP response.

CONCLUSIONS

By using microarrays to assess multiple genes in a high throughput manner, we demonstrate that an inflammatory response involving different dynamics and different genes is triggered by SCLP and CLP. From our analysis of the CLP data, the key characteristics of sepsis are a proinflammatory response, which drives hypermetabolism, immune cell activation, and damage from oxidative stress. This contrasts with SCLP, which triggers a modified inflammatory response leading to no immune cell activation, decreased detoxification potential, and hyper metabolism. Many of the identified transcription factors that drive the CLP-induced response are not found in the SCLP group, suggesting that SCLP and CLP induce different types of inflammatory responses via different regulatory pathways.

Interspecies difference in liver-specific functions and biotransformation of testosterone of primary rat, porcine and human hepatocyte in an organotypical sandwich culture

Interspecies difference is an important issue in toxicology research. We compared the potential in vitro metabolism of human, porcine and rat hepatocytes over 2 weeks in culture in an organotypical culture model which reflects the in vivo situation. All three species show similar LDH-rates. Albumin measurements showed that rat cells are about twice as active as human and porcine hepatocytes. The ethoxyresorufin-O-deethylase (EROD) activity of the rat hepatocytes is with about 14 microU/10(6)cells distinctly higher than those of porcine and human cells (1.8 and 0.5 microU/10(6)cells respectively), furthermore, the activity of the rat EROD increases slightly during the prolonged time in culture, whereas those of porcine and human enzymes slightly decrease. Concerning ethoxycoumarin-O-deethylase (ECOD), the enzyme activities are found to be in three different ranges where rat cells show the highest activity with 66 microU/10(6)cells, porcine hepatocytes exhibit an activity of about 23 microU/10(6)cells, and human activity is lowest with 0.7 microU/10(6)cells. All three species show a similar decreasing trend of ECOD during the period of study. Regarding the biotransformation of testosterone, human and porcine liver cells form three major metabolites whereas rat cells form a mixture of all measured metabolites. Hence, in vitro metabolism using porcine hepatocytes would be much more scientific sense than one using rat hepatocytes since the metabolic pathways are much closer to human metabolism.

Clinical versatility of porcine hepatocytes in the light of interspecies differences in cytochrome P450 regulation and expression

BACKGROUND AND AIMS

In fulminant hepatic failure, the clinical use of bioartifical liver support with porcine hepatocytes is the subject of a controversial debate. Cytochrome P450 (CYP) metabolic functions have relevant implications for drug metabolism and detoxification. In this study, we investigate interspecies differences in CYP gene expression between human and porcine primary hepatocytes and the impact of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) exposition mimicking cytokine release in fulminant hepatic failure.

METHODS

Primary hepatocyte cultures were isolated from human resection specimens and from German landrace pigs. Cell cultures (single and co-cultures) were exposed to porcine vs. human IL-6 and TNF-alpha, respectively. Changes in quantitative CYP gene expression were investigated by semi-quantitative RT-PCR.

RESULTS

Significant differences in species-specific CYP gene expression by human and porcine hepatocytes were found after exposure to species-identical IL-6 (10 ng/ml) for CYP 1A1, CYP 2C, CYP 3A (P = 0.002, 0.022, 0.017, respectively) or species-identical TNF-alpha (30 ng/ml) for CYP 1A2 and CYP 2A (P = 0.037, 0.023, respectively). In single vs. co-culture, human hepatocytes demonstrated stronger repression of CYP 1A1, 2C8 and 3A4 expression after dosage with human IL-6 (10 ng/ml) (P = 0.022, 0.031, 0.014, respectively).

CONCLUSION

Our findings demonstrate significant species-specific differences in CYP gene expression and regulation when high doses of IL-6 and TNF-alpha are used (10 and 30 ng/ml, respectively). These findings may point to species-specific physiological incompatibilities of porcine hepatocytes and thus limit their clinical versatility.

Permissive and suppressive effects of dexamethasone on enzyme induction in hepatocyte co-cultures

1. Steroids are known to act as permissive factors in hepatocytes. This study shows that dexamethasone (DEX) is a permissive factor for induction of CYP2B1/2, CYP3A1, CYP2A1 and probably also CYP2C11 in cultures with primary rat hepatocytes. 2. The induction factor of phenobarbital (PB)-induced formation of 16beta-hydroxytestosterone (OHT), a testosterone biotransformation product predominantly formed by CYP2B1, is increased 18-fold by the addition of 32 nM DEX to the culture medium. Interestingly, higher concentrations of DEX up to 1000 nM led to a concentration-dependent maximally 5-fold decrease (p = 0.002) of phenobarbital-induced 16beta-OHT formation compared with the effect observed with 32 nM DEX. Thus, DEX shows permissive and suppressive effects on enzyme induction depending on the concentration of the glucocorticoid. 3. Qualitatively similar but smaller permissive and suppressive effects of DEX were observed for PB-induced CYP3A1 activity as evidenced by formation of 2beta-, 6beta- and 15beta-OHT. 4. DEX is a permissive factor for induction of CYP2A1 activity by 3-methylcholanthrene (3MC), as evidenced by the formation of 7alpha-OHT. Without addition of DEX, 3MC did not induce formation of 7alpha-OHT, whereas an almost 3-fold induction occurred in the presence of DEX. In contrast to CYP2B and CYP3A, concentrations up to 1000 nM DEX were not suppressive for the induction of CYP2A1. 5. We described recently a technique that allows preparation of cultures from cryopreserved hepatocytes. An almost identical influence of dexamethasone on enzyme induction was observed here in cultures from cryopreserved compared with freshly isolated hepatocytes. 6. Cultures with primary hepatocyte cultures represent a well-established technique for the study of drug-drug interactions. However, a large interlaboratory variation is known. Our study provides evidence that differences in glucocorticoid concentration in the culture medium contribute to this variation.

Biotransformation of cyclosporin in primary rat, porcine and human liver cell co-cultures

The purpose of this study was to investigate the species-specific cyclosporin biotransformation in primary rat, human, and porcine liver cell cultures, and to investigate the suitability of a modified sandwich culture technique with non-purified liver cell co-cultures for drug metabolism studies. A sandwich culture was found to enhance hepatocellular metabolic activity and improve cellular morphology and ultrastructure. The cyclosporin metabolites AM9 and AM1 were formed in porcine and human liver cell sandwich co-cultures at levels corresponding to the respective in vivo situations. In contrast, metabolite profiles in rat hepatocytes were at variance with the in vivo situation. However, for all cell types, the overall metabolic activity was positively influenced by sandwich co-culture. The initial levels of albumin synthesis were higher in sandwich cultures than in those without matrix overlay. It is hypothesized that the sandwich culture system provides an improved microenvironment and is, therefore, an advantageous tool for in vitro studies of drug metabolism.

Morphological and phenotypic characteristics of human fetal hepatocytes in different culture medium

AIM: To explore an optimal culture condition for human fetal hepatocytes (HFHs).

METHODS: A two-step collagenase perfusion technique was used to isolate HFHs. The freshly isolated cell suspension was purified by means of discontinuous Percoll density gradients centrifugation. After purification, cells were cultured in Ham's F12 medium or Ham's F12 hormonally defined medium for different time respectively, and the specific expression of cytokeratin 18 (CK18) and alpha-1-fetoprotein (AFP) in the primary cultures was characterized by indirect immunofluorescence method. Cell growth and proliferation was checked by MTT method.

RESULTS: In the condition of Ham's F12 hormonally defined medium, HFHs exhibited typical hepatocyte-specific polygonal morphology; the cultures consisted of 100% CK18- and AFP-positive cells during different time; HFHs retained higher proliferative potential. However, in the condition of Ham's F12 medium, some cells in the cultures showed a sharp and spindle feature, and only 56% cells of the cultures expressed CK18 and 43% expressed AFP at the 24th hour. And at the 72nd hour, all cells presented a sharp and spindle feature, and had poorer proliferative potential and viability (0.25 ± 0.03 vs 1.01 ± 0.12, P < 0.001). On the 7th day, there were not CK18- and AFP-positive cells in the cultures, and the cells had worst proliferative potential and viability (0.17 ± 0.04 vs 0.94 ± 0.12, P < 0.001).

CONCLUSION: Using Ham's F12 hormonally defined medium, we are able to maintain the specific polygonal morphology and stable phenotype of primary HFHs for 1 week, and moreover, the cells retain a higher proliferative potential.

Development and characterization of a small-scale bioreactor based on a bioartificial hepatic culture model for predictive pharmacological in vitro screenings

A vast majority of pharmacons are beset by possible interactions and side effects which have usually been tested in laboratory animals. However, better methods are needed to reduce the number of animal experiments and interspecies differences with respect to drug metabolism, as well as to provide a faster and more cost-effective way of analysis. These facts have led to the development of in vitro models based on isolated primary hepatocytes to better assess drug metabolism, interactions, and toxicity. A new small-scale bioreactor with the hepatic sandwich model and a gas-permeable membrane at the bottom allowing a definable oxygen exchange, has been constructed and compared with the conventional well plates. Compared to hepatocytes cultured in conventional systems, the cells exhibited a stronger liver-specific capacity and remained in a differentiated state in the small-scale bioreactor over a cultivation period of 17 days. This in vitro model could serve as a tool to predict the liver response to newly developed drugs.

A high-throughput microfluidic real-time gene expression living cell array

The dynamics of gene expression are fundamental to the coordination of cellular responses. Measurement of temporal gene expression patterns is currently limited to destructive low-throughput techniques such as northern blotting, reverse transcription polymerase chain reaction (RT-PCR), and DNA microarrays. We report a scalable experimental platform that combines microfluidic addressability with quantitative live cell imaging of fluorescent protein transcriptional reporters to achieve real-time characterization of gene expression programs in living cells. Integrated microvalve arrays control row-seeding and column-stimulation of 256 nanoliter-scale bioreactors to create a high density matrix of stimulus-response experiments. We demonstrate the approach in the context of hepatic inflammation by acquiring approximately 5000 single-time-point measurements in each automated and unattended experiment. Experiments can be assembled in hours and perform the equivalent of months of conventional experiments. By enabling efficient investigation of dynamic gene expression programs, this technology has the potential to make significant impacts in basic science, drug development, and clinical medicine.

Physiological incompatibilities of porcine hepatocytes for clinical liver support

In fulminant hepatic failure, the use of bioartificial liver support (BAL) with porcine hepatocytes is the subject of a current and controversial debate.1 Specifically, the issue of cross-species physiological incompatibilities has not been addressed so far. We therefore investigated the effects of species-specific cytokines in single and cocultures on hepatocyte function. Hepatocyte cultures were isolated from human resection specimens and from Landrace pigs. Single and cocultures were exposed to porcine and human interleukin (IL)-6 or tumor necrosis factor (TNF)-alpha. Changes in expression of C-reactive protein (CRP), albumin, CCAAT enhancer binding protein (C/EBP)-alpha and C/EBP-beta and metabolic competence of cultured cells was studied by measuring testosterone metabolite production. After human or porcine IL-6 dosing, CRP was induced up to 100-fold in human hepatocyte cultures, while porcine hepatocytes responded marginally (2- to 5-fold). Treatment with human or porcine IL-6 or TNF-alpha resulted in reduced albumin production, albeit at different levels when human and porcine hepatocytes were compared (P = 0.001). Unlike human, porcine hepatocytes produced less of 6alpha-hydroxytestosterone (6alpha-HT) (P < 0.001) and 7alpha-HT (P < 0.001) after human or porcine IL-6 dosing and treatment with species-specific TNF-alpha induced (human hepatocytes) or decreased (porcine hepatocytes) 6beta-HT production (P = 0.021). In coculture with free exchange of metabolites, porcine hepatocytes produced less 6alpha-HT (P = 0.048) and 16alpha-HT (P = 0.033), whereas after treatment with human IL-6 reduced CRP gene and protein expression was observed with human hepatocytes (P = 0.013). In conclusion, species-specific responses of hepatocytes to cytokines and interactions with xenobiotic metabolites may limit the clinical effectiveness of porcine hepatocytes in BAL.

Present and Future Developments in Hepatic Tissue Engineering for Liver Support Systems : State of the art and future developments of hepatic cell culture techniques for the use in liver support systems

The liver is the most important organ for the biotransformation of xenobiotics, and the failure to treat acute or acute-on-chronic liver failure causes high mortality rates in affected patients. Due to the lack of donor livers and the limited possibility of the clinical management there has been growing interest in the development of extracorporeal liver support systems as a bridge to liver transplantation or to support recovery during hepatic failure. Earlier attempts to provide liver support comprised non-biological therapies based on the use of conventional detoxification procedures, such as filtration and dialysis. These techniques, however, failed to meet the expected efficacy in terms of the overall survival rate due to the inadequate support of several essential liver-specific functions. For this reason, several bioartificial liver support systems using isolated viable hepatocytes have been constructed to improve the outcome of treatment for patients with fulminant liver failure by delivering essential hepatic functions. However, controlled trials (phase I/II) with these systems have shown no significant survival benefits despite the systems' contribution to improvements in clinical and biochemical parameters. For the development of improved liver support systems, critical issues, such as the cell source and culture conditions for the long-term maintenance of liver-specific functions in vitro, are reviewed in this article. We also discuss aspects concerning the performance, biotolerance and logistics of the selected bioartificial liver support systems that have been or are currently being preclinically and clinically evaluated.

Constitutive secretion of serum albumin requires reversible protein tyrosine phosphorylation events intrans-Golgi

Serum albumin secretion from rat hepatocytes proceeds via the constitutive pathway. Although much is known about the role of protein tyrosine phosphorylation in regulated secretion, nothing is known about its function in the constitutive process. Here we show that albumin secretion is inhibited by the tyrosine kinase inhibitor genistein but relatively insensitive to subtype-selective inhibitors or treatments. Secretion is also blocked in a physiologically identical manner by the tyrosine phosphatase inhibitors pervanadate and bisperoxo(1,10-phenanthroline)-oxovanadate. Inhibition of either the kinase(s) or phosphatase(s) leads to the accumulation of albumin between the trans-Golgi and the plasma membrane, whereas the immediate precursor proalbumin builds up in a proximal compartment. The trans-Golgi marker TGN38 is rapidly dispersed under conditions that inhibit tyrosine phosphatase action, whereas the distribution of the cis-Golgi marker GM130 is insensitive to genistein or pervanadate. By using a specifically reactive biotinylation probe, we detected protein tyrosine phosphatases in highly purified rat liver Golgi membranes. These membranes also contain both endogenous tyrosine kinases and their substrates, indicating that enzymes and substrates for reversible tyrosine phosphorylation are normal membrane-resident components of this trafficking compartment. In the absence of perturbation of actin filaments and microtubules, we conclude that reversible protein tyrosine phosphorylation in the trans-Golgi network is essential for albumin secretion and propose that the constitutive secretion of albumin is in fact a regulated process.

Induction of a hypermetabolic state in cultured hepatocytes by glucagon and H2O2

Stress hormones and pro-inflammatory cytokines are putative signals triggering increased energy expenditure or "hypermetabolism" commonly observed in inflammatory states. Cytokines also cause the release of reactive oxidants by immune cells resident in tissues in vivo. Therefore, we hypothesized that oxidative stress plays a role in the induction of hypermetabolism. We examined the effect of glucagon (1.0 nM), a catabolic stress hormone, and the oxidant H(2)O(2) (1.0 mM) on the metabolism of stable hepatocyte cultures for 4 days. Combined H(2)O(2) and glucagon treatment, but not H(2)O(2) or glucagon used alone, increased the hepatocyte oxygen uptake rate 25% above control untreated cells after a lag-time of 72 h. The same treatment also increased the expression of mitochondrial uncoupling protein-2 (UCP2). These effects were significantly inhibited by the antioxidant N-acetylcysteine (5mM) and the pentose phosphate pathway (PPP) inhibitor dehydroepianderosterone (200 microM). Glucagon alone induced urea synthesis and H(2)O(2) alone induced the PPP. These findings show, for the first time, that oxidative stress, in combination with glucagon, increases metabolic energy expenditure in cultured cells, and that this effect may be mediated by UCP-2. Furthermore, the results implicate the PPP in the induction of the hypermetabolic response.

Comparison of primary human hepatocytes and hepatoma cell line Hepg2 with regard to their biotransformation properties

Cultures of primary hepatocytes and hepatoma cell line HepG2 are frequently used in in vitro models for human biotransformation studies. In this study, we characterized and compared the capacity of these model systems to indicate the presence of different classes of promutagens. Genotoxic sensitivity, enzyme activity, and gene expression were monitored in response to treatment with food promutagens benzo[a]pyrene, dimethylnitrosamine (DMN), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). DNA damage could be detected reliably with the comet assay in primary human hepatocytes, which were maintained in sandwich culture. All three promutagens caused DNA damage in primary cells, but in HepG2 no genotoxic effects of DMN and PhIP could be detected. We supposed that the lack of specific enzymes accounts for their inability to process these promutagens. Therefore, we quantified the expression of a broad range of genes coding for drug-metabolizing enzymes with real-time reverse transcription-polymerase chain reaction. The genes code for cytochromes p450 and, in addition, for a series of important phase II enzymes. The expression level of these genes in human hepatocytes was similar to those previously reported for human liver samples. On the other hand, expression levels in HepG2 differed significantly from that in human. Activity and expression, especially of phase I enzymes, were demonstrated to be extremely low in HepG2 cells. Up-regulation of specific genes by test substances was similar in both cell types. In conclusion, human hepatocytes are the preferred model for biotransformation in human liver, whereas HepG2 cells may be useful to study regulation of drug-metabolizing enzymes.

Control analysis of mitochondrial metabolism in intact hepatocytes: effect of interleukin-1beta and interleukin-6

Interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) are produced by hepatic nonparenchymal cells after systemic injury and have been reported to inhibit ATP synthesis in hepatocytes, which may contribute to hepatic dysfunction in inflammatory states. To elucidate the mechanisms of action of IL-1beta and IL-6 on hepatocellular ATP synthesis, we measured the oxygen uptake rate (OUR) and mitochondrial membrane potential (MMP) of stable hepatocyte cultures, and analyzed the dynamic MMP response following the addition of mitochondrial inhibitors (antimycin A and oligomycin) with a model of mitochondrial metabolism. IL-1beta reduced mitochondrial OUR coupled to ATP synthesis via inhibition of phosphorylation reactions which dissipate the MMP, including ATP synthesis and consumption. Furthermore, the ATP synthesis rate in cytokine-free and IL-1beta-treated hepatocytes was controlled primarily by phosphorylation reactions, which corresponds to a state where the ATP synthesis rate closely follows the cellular energy demand. Thus, IL-1beta-mediated effects on electron transport and substrate oxidation reactions are not likely to significantly impact on ATP synthesis. IL-6 did not reduce mitochondrial OUR coupled to ATP synthesis, but shifted the control for ATP synthesis towards processes which generate the MMP, indicating that IL-6 induces a metabolic state where cellular functions are limited by the mitochondrial energy supply.

Evaluation of a galactose-carrying gelatin sponge for hepatocytes culture and transplantation

This study proposes a new three-dimensional culture of mouse hepatocytes in a porous galactose-carrying modified gelatin sponge matrix. The modification of gelatin using galactose residues significantly increased the attachment of hepatocytes on the substrate. A modified gelatin sponge with lactobionic acid (MGLA) was prepared to increase the specific interaction between the hepatocytes and the matrix. Hepatocytes cultured in a three-dimensional MGLA sponge released much less lactate dehydrogenase than those cultured on a collagen Type I-coated monolayer. Moreover, the survival rate of hepatocytes cultured on an MGLA sponge was longer than the survival rate of hepatocytes cultured on a collagen Type I-coated monolayer. Hepatic specific metabolic functions, namely, the secretion of serum albumin and the synthesis of urea, were well maintained and promoted by spheroidal hepatocytes formed in the MGLA sponge.

Long-term stable cultures of rat hepatocytes: an in vitro model to study acute and chronic hepatic inflammation

Engineered tissues provide an opportunity to investigate important physiological processes difficult to study in whole perfused organs and animal models. For example, a hepatocyte culture model consisting of rat hepatocytes cultured in a collagen sandwich configuration, which exhibits stable differentiated liver-specific functions, may be useful to investigate liver pathophysiology. To investigate systemic inflammation-related hepatic failure, we chronically exposed hepatocytes to the inflammatory mediators interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) for up to 4 weeks. IL-6 (2.5 ng/mL) transiently suppressed albumin (-90%) and chronically increased fibrinogen (+6-fold) production. IL-6 inhibited urea synthesis at 2.5 ng/mL and stimulated it at 0.025 ng/mL. IL-1beta (10 ng/mL) inhibited albumin (-90%), urea (-40 to 50%), and IL-6-stimulated fibrinogen (-90%) secretion. The inhibitory effect of IL-1beta on urea secretion was dose-dependent. Furthermore, IL-1beta transiently stimulated nitric oxide (NO) synthesis; however, NO did not mediate the effect of IL-1beta on albumin and fibrinogen production, and played a minor role in IL-1beta-mediated urea synthesis suppression. In conclusion, IL-1beta and IL-6 exert, via a direct effect on hepatocytes, long-term inhibitory effects on hepatic functions that are potentially important for the survival of the host, which may contribute to hepatic dysfunction in prolonged inflammatory states.

Longterm stability of phase I and phase II enzymes of porcine liver cells in flat membrane bioreactors

Recently, researchers have focused on the use of bioartificial liver devices to support patients with fulminant hepatic failure. Our team developed a cell-based flat membrane bioreactor (FMB). In this, porcine liver cells were maintained in 3D-coculture between two gel layers in a sandwich configuration for 3 weeks to study the influence of this bioreactor technique on the preservation of basic, not induced activities of phase I and phase II enzymes. First, the time and substrate dependencies of the following enzymes were measured: ethoxyresorufin-O-deethylase (EROD, CYP 1A1/1A2) and ethoxycoumarin-O-deethylase (ECOD, CYP 2B6) as phase I enzymes, and glutathione-S-transferase (GST), UDP-glucuronosyltransferase (UGT) and sulfotransferase (ST) as phase II enzymes. To find optimal test conditions Michaelis-Menten kinetics were calculated. Next, different potential inducers were tested to find out the most effective compounds. Based on these results, the basic, not induced levels of the different enzymes were determined in the flat membrane bioreactor. Furthermore, the response of these enzyme activities to the chosen inducers was investigated to examine whether the cells keep their ability for drug-drug interactions. Basic, not induced activities of both phase I enzymes and the phase II enzymes GST and UGT were maintained at nearly the initial levels during the complete period of study. In addition, it was possible to induce these enzymes twice or three times in a weekly interval. In contrast, the basic, not induced activity of ST increased during the first 10 days of culture. It stabilized then and was maintained steady. As in short-term investigations, no reaction of the ST-activity towards any inducer could be obtained. These results prove that porcine liver cells preserve their phase I and phase II activities and respond to inducing drugs over 3 weeks in culture. Therefore, the flat membrane bioreactor is not only suitable for investigating drug metabolism, drug-drug interactions, and enzyme induction but also for supporting liver functions.

Interleukin-6 stimulates hepatic insulin-like growth factor binding protein-4 messenger ribonucleic acid and protein

Sepsis and bacterial lipopolysaccharide (LPS) injection decrease circulating concentrations of insulin-like growth factor (IGF)-I and induce an increase in IGFBP-1 and IGFBP-4 that may have impact upon IGF-I anabolic actions. Although the mechanisms responsible for the IGFBP-1 increase in response to LPS have already been unraveled, the cause for the IGFBP-4 elevation is still unknown. The aim of this study was to characterize the regulation of IGFBP-4 by proinflammatory cytokines and glucocorticoids. In rat primary cultured hepatocytes, interleukin (IL)-6 strongly stimulated IGFBP-4 messenger RNA (mRNA) and protein levels in a dose- and time-dependent way (mRNA levels: 9-fold, P: < 0.01 and protein levels: approximately 3-fold at 24 h, with IL-6 10 ng/ml). Interleukin (IL)-1ss and tumor necrosis factor (TNF)-alpha blunted the IL-6 stimulation of IGFBP-4 mRNA (66% and 46% decrease, respectively) and protein levels (82% and 68% decrease, respectively). In contrast, dexamethasone induced IGFBP-4 mRNA and protein and potentiated the effect of IL-6 on IGFBP-4 mRNA (2.5-fold, P: < 0.01 vs. IL-6 alone). Both actinomycin and cycloheximide prevented the IL-6 induction of IGFBP-4 mRNA suggesting that the IL-6 effect on IGFBP-4 gene occurs probably at the transcriptional level and needs an ongoing protein synthesis. Administration of IL-6 to rats caused a 3-fold increase in liver IGFBP-4 mRNA (P: < 0.001) reflected in serum levels of IGFBP-4 (P: < 0.05). In conclusion, our results show that IL-6 stimulates hepatic IGFBP-4 gene expression and production in vitro and in vivo, thereby suggesting another mechanism by which cytokines could control IGF-I action.

Dynamics of gene expression in rat hepatocytes under stress

The response of cells to physical or biochemical stress involves concerted changes in the expression of a large number of genes encoding various functions. We have used a quantitative kinetic RT-PCR technique to follow the dynamics of changes in transcription factor and acute-phase mRNA levels in cultured rat hepatocytes subjected to either elevated temperature (40 degrees C) or exposure to the inflammatory cytokine interleukin-6. The profiles of transcription factor gene expression displayed rapid and coordinate regulation, attainment of new steady-states, transitions in some instances from up-regulation to down-regulation (or vice versa), and, for elevated temperature, multiple spikes of up-regulation. Transcripts of acute-phase genes generally displayed relatively small changes during the first few hours followed by more significant changes over the course of tens of hours (elevated temperature) to days (IL-6 exposure). These observations are all consistent with the notion of genetic reprogramming due to a network of interacting transcription factor proteins and transcripts. We utilized a simple transcription/translation model incorporating autoregulation to describe the dynamics of transcription factor gene expression. This model successfully described key features of the transcription factor dynamics, most notably the multiple spikes observed after exposure to elevated temperature. The dynamics of gene expression are rich in information that, with considerably more study, may eventually be exploited to provide insights into the interplay of genetic networks in regulating a variety of cellular responses.

In vitro model of the human liver parenchyma to study hepatotoxic side effects by Dy-EOB-DTPA

RATIONALE AND OBJECTIVES

In vivo studies have shown species-specific toxicity after application of the liver-specific contrast agent Dy-ethoxybenzyl (EOB)-DTPA. To predict species differences in the laboratory, an in vitro model of the liver was used to examine the divergent results.

METHODS

Rat, canine, porcine, and human hepatocytes were isolated and embedded between layers of collagen. During and after 48 hours of incubation with different concentrations of Dy-EOB-DTPA (maximum concentration 50 mmol/L), morphological changes and enzyme leakage were determined.

RESULTS

The response to the contrast agent varied for hepatocytes from different species. For canine cells, morphological changes and cell death were evident with as little as 5 mmol/L Dy-EOB-DTPA. Rat hepatocytes tolerated up to 50 mmol/L Dy-EOB-DTPA, and enzyme leakage was transient. Only after incubation with 50 mmol/L Dy-EOB-DTPA was the formation of intracellular vacuoles evident. In contrast, even the highest concentration of Dy-EOB-DTPA did not cause an enzyme leakage of porcine or human hepatocytes, although similar vacuoles were seen.

CONCLUSIONS

These data demonstrate a species-dependent toxicity for Dy-EOB-DTPA in vitro, with similar responses in porcine and human hepatocytes.

Hepatocyte behavior within three-dimensional porous alginate scaffolds

A potential approach to facilitate the performance of implanted hepatocytes is to enable their aggregation and re-expression of their differentiated function prior to implantation. Here we examined the behavior of freshly isolated rat adult hepatocytes seeded within a novel three-dimensional (3-D) scaffold based on alginate. The attractive features of this scaffold include a highly porous structure (sponge-like) with interconnecting pores, and pore sizes with diameters of 100-150 microm. Due to their hydrophilic nature, seeding hepatocytes onto the alginate sponges was efficient. DNA measurements showed that the total cell number within the sponges did not change over 2 weeks, indicating that hepatocytes do not proliferate under these culture conditions. Nearly all seeded cells maintained viability, according to the MTT assay. Within 24 h post-seeding, small clusters of viable cells, were seen scattered within the sponge. More than 90% of the seeded cells participated in the aggregation; the high efficiency is attributed to the non-adherent nature of alginate. The spheroids had smooth boundaries and by day 4 in culture reached an average diameter of 100 microm, which is at the same magnitude of the sponge pore size. The cells appeared to synthesize fibronectin which was deposited on the spheroids. No laminin or collagen type IV were detected in the deposit. The 3-D arrangement of hepatocytes within the alginate sponges promoted their functional expression; within a week the cells secreted the maximal albumin secretion rate of 60 microg albumin/10(6) cells/day. Urea secretion rate did not depend on cell aggregation and was similar to that obtained when hepatocytes were cultured on collagen type I coated dishes (100 microg/10(6) cells/day). Our studies show that alginate sponges can provide a conducive environment to facilitate the performance of cultured hepatocytes by enhancing their aggregation.

Cryopreserved primary hepatocytes as a constantly available in vitro model for the evaluation of human and animal drug metabolism and enzyme induction

The use of primary hepatocytes is now well established for both studies of drug metabolism and enzyme induction. Cryopreservation of primary hepatocytes decreases the need for fresh liver tissue. This is especially important for research with human hepatocytes because availability of human liver tissue is limited. In this review, we summarize our research on optimization and validation of cryopreservation techniques. The critical elements for successful cryopreservation of hepatocytes are (1) the freezing protocol, (2) the concentration of the cryoprotectant [10% dimethyl-sulfoxide (DMSO)], (3) slow addition and removal of DMSO, (4) carbogen equilibration during isolation of hepatocytes and before cryopreservation, and (5) removal of unvital hepatocytes by Percoll centrifugation after thawing. Hepatocytes of human, monkey, dog, rat, and mouse isolated and cryopreserved by our standard procedure have a viability > or = 80%. Metabolic capacity of cryopreserved hepatocytes determined by testosterone hydroxylation, 7-ethoxyresorufin-O-de-ethylase (EROD), 7-ethoxycoumarin-O-deethylase (ECOD), glutathione S-transferase, UDP-glucuronosyl transferase, sulfotransferase, and epoxide hydrolase activities is > or = 60% of freshly isolated cells. Cryopreserved hepatocytes in suspension were successfully applied in short-term metabolism studies and as a metabolizing system in mutagenicity investigations. For instance, the complex pattern of benzo[a]pyrene metabolites including phase II metabolites formed by freshly isolated and cryopreserved hepatocytes was almost identical. For the study of enzyme induction, a longer time period and therefore cryopreserved hepatocyte cultures are required. We present a technique with cryopreserved hepatocytes that allows the induction of testosterone metabolism with similar induction factors as for fresh cultures. However, enzyme activities of induced hepatocytes and solvent controls were smaller in the cryopreserved cells. In conclusion, cryopreserved hepatocytes held in suspension can be recommended for short-term metabolism or toxicity studies. Systems with cryopreserved hepatocyte cultures that could be applied for studies of enzyme induction are already in a state allowing practical application, but may be further optimized.

Investigation of albumin-synthesizing ability in rat cirrhotic liver-derived hepatocytes using primary hepatocyte culture

BACKGROUND/AIMS

In cirrhosis, despite a decrease in the total number of hepatocytes, a normal serum albumin level is maintained during the compensatory stage of the disease in many cases. Therefore, to elucidate the mechanism in hepatocytes related to the regulation of the serum albumin level, the albumin-synthesizing ability of individual hepatocytes was investigated in cirrhotic rats.

METHODS

Cirrhotic rats were prepared by oral administration of furfural to male Wistar rats for 20 weeks. Albumin-synthesizing abilities of liver and of isolated hepatocyte culture were evaluated by measuring the albumin concentration in blood and culture supernatant. Expressions of albumin mRNA were compared using Northern blotting. Furthermore, transcriptional activity of the albumin gene was measured using the promoter domain of the gene.

RESULTS

The total number of hepatocytes in rat cirrhotic liver was significantly decreased compared to that in normal rat liver. However, there were no significant differences in levels of serum albumin or albumin mRNA expression between cirrhotic and normal liver. In primary hepatocyte culture, albumin mRNA expression, the amount of albumin secretion and the albumin promoter activity were clearly enhanced in cirrhotic hepatocytes compared to normal hepatocytes.

CONCLUSION

Although the total number of hepatocytes was decreased in the rat cirrhosis models used in this study, the serum albumin level was maintained and albumin-synthesizing ability was enhanced at the transcriptional level in the individual hepatocytes. These results suggest that the maintenance of serum albumin levels in compensated cirrhosis may be due to enhanced albumin synthesis by the hepatocytes.

Acute-phase response patterns in isolated hepatic perfusion with tumour necrosis factor alpha (TNF-alpha) and melphalan in patients with colorectal liver metastases

BACKGROUND

In this study, we have evaluated hepatotoxicity, secondary cytokine production and hepatic acute-phase response (APR) in patients who underwent isolated hepatic perfusion (IHP) with tumour necrosis factor (TNF) alpha and melphalan for irresectable colorectal liver metastases.

DESIGN

An extracorporeal veno-venous bypass was used to shunt blood from the lower body and intestines to the heart. Inflow catheters were placed in the hepatic artery and portal vein, and an outflow catheter in the inferior caval vein. The liver was perfused for 60 min with 0.4 mg of TNF-alpha plus 1 mg kg-1 melphalan (IHPTM group, n = 6) or 1 mg kg-1 melphalan (IHPM group, n = 3). The liver was washed with macrodex before restoring vascular continuity.

RESULTS

After the washout procedure, a TNF-alpha peak (169 +/- 38 pg mL-1) was demonstrated in the IHPTM group only. Both groups demonstrated peak levels of interleukin 6 (IL-6) in the perfusate as well as systemically. These were significantly higher in the IHPTM group. Acute-phase protein (APP) levels followed a similar pattern as has been demonstrated after major surgery, with no significant differences between both groups. The addition of TNF-alpha to the perfusate did not lead to a significant difference in APP levels and the time course between groups.

CONCLUSIONS

IHP with TNF and melphalan is followed by a transient systemic peak of TNF directly after liver washout. Secondary IL-6 induction was seen in the present study after IHP with and without TNF, which was highest when TNF was added. This phenomenon cannot be extrapolated to APP induction, which appeared unaffected by the addition of TNF, presumably because the surgical procedure itself already causes maximal stimulation of APP production.

Enhanced oxygen delivery reverses anaerobic metabolic states in prolonged sandwich rat hepatocyte culture

It must be assumed that current petri dish primary hepatocyte culture models do not supply sufficient amounts of oxygen and thus cause anaerobic metabolism of the cells. This is contrary to the physiologic state of the cells. In vivo the liver is a highly vascularized organ with a rather high blood flow rate of a mixture of arterial and venous blood. The aim of the present study was to show the oxygen dependence of primary rat hepatocytes in long-term culture and to define appropriate conditions that could allow hepatocytes to maintain tissue specific functions in an aerobic environment. To this purpose matrix overlaid hepatocytes were either cultured on gas-permeable (fluorinated hydrocarbon films) or gas-impermeable (polystyrene) supports at 10% and 20% ambient oxygen concentration (v/v), respectively. Tissue-specific functions were assessed by studying albumin and urea secretion as well as xenobiotic metabolism. The mRNA expression and catalytic activities of the cytoprotective antioxidant enzymes mitochondrial manganese superoxide dismutase (MnSOD), cytosolic copper and zinc superoxide dismutase, peroxisomal catalase, and cytosolic glutathione peroxidase were investigated to assess intracellular responses to the defined variations in oxygen supply. Hepatocytes could successfully be maintained at aerobic conditions in long-term culture on gas-permeable PTFE films. At 50% (10%, v/v) of currently used oxygen levels lactate accumulation was prevented, a plateau-like albumin secretion reestablished, urea secretion improved, and xenobiotic metabolism proceeded at physiological rates. mRNA expression of cytoprotective enzymes responded to the pericellular availability of oxygen and was most pronounced in the case of MnSOD. However, the biggest stress factor for the hepatocytes still appeared to be the isolation procedure, as mRNA expression and catalytic activities were most elevated shortly thereafter. In conclusion, this study clearly shows the oxygen dependence of primary rat hepatocytes in long-term culture and indicates means to establish appropriate conditions for the aerobic culture of primary rat sandwich hepatocytes with full maintenance of function. The long-term culture of hepatocytes on oxygenating supports at in vivo-like oxygen tensions therefore appears to be more physiologic and beneficial for the cells.

Interaction between heat shock and interleukin 6 stimulation in the acute-phase response of human hepatoma (HepG2) cells

Two characteristic elements of the acute-phase response are an altered pattern of circulating hepatic proteins and fever. Whereas a fever-induced heat shock response could affect expression of acute-phase proteins in the liver, the effects of a modest temperature increase on protein secretion in interleukin-6 (IL-6)-stimulated HepG2 cells were investigated. The response of HepG2 cells to IL-6 stimulation was significantly affected by heat treatment at 40 degreesC. Albumin secretion rates, which were reduced by a factor of 2 in response to either heat shock or IL-6 stimulation alone, were down-regulated by a factor of 4 when IL-6 was administered simultaneously with a continuous 40 degrees C heat shock. IL-6-induced fibrinogen up-regulation was significantly reduced by heat treatment (P < .01), and secretion rates were indistinguishable from control levels after 2 days (P > .10). Unexpectedly, heat shock at 40 degrees C induced a fivefold up-regulation of haptoglobin production in the absence of IL-6. Simultaneous heat shock and IL-6 stimulation caused a synergistic enhancement of haptoglobin expression, with secretion rates increasing up to 30-fold compared with unstimulated control cells. For all three proteins, the interaction between temperature and IL-6 concentration was statistically significant (P < .001). Heat treatment resulted in significant alterations of both the kinetics and sensitivity of IL-6-induced protein synthesis, suggesting a major modification of the mechanism of acute-phase protein regulation at 40 degreesC. In summary, the data show that heat shock can significantly modulate the pattern of acute-phase protein expression and that fever may be an important regulatory factor in the acute-phase response.

Preclinical assessment of hepatocyte-targeted MR contrast agents in stable human liver cell cultures

Much effort has been expended in the search for hepatocyte-specific MR contrast agents to improve the detection and characterization of liver tumors. The purpose of this study was to establish human hepatocyte cell cultures to preclinically assess hepatocyte-targeted magnetopharmaceuticals. Cultured human hepatocytes were sandwiched between two layers of collagen preserving both hepatocyte function and morphology over prolonged period of time. Cultures (n = 37) were subsequently used to test different fluorescinated MR contrast agents. Plain and rhodaminated monocrystalline iron oxide particles (MION and MION-rh) and asialoglycoprotein-receptor-specific rhodaminated asialofetuin coupled to MION (MION-ASF-rh) were prepared. Competition experiments of these agents were performed with D(+)-galactose to study the specificity of galactose-mediated cell uptake. To assess the impact of cell integrity on cell uptake, functional experiments with CCl4 were performed. Normal cell cultures showed significantly higher fluorescence light emission after incubation with hepatocyte-directed ASF-MION-rh than after incubation with MION-rh. Competition experiments of ASF-MION-rh with galactose showed a dose-dependent decrease of calibrated fluorescence light emission. Cell cultures treated with CCl4 demonstrated a dose-dependent significant reduction of calibrated fluorescence light emission, indicating reduced uptake of ASF-MION-rh. Our data demonstrate that stable human hepatocyte cell cultures can be used to preclinically assess novel magnetopharmaceuticals. Different contrast agents may be directly compared to each other and may accelerate their preclinical design. Because the assay can be applied to cells from any species, it may represent an ideal test system before clinical trials of new cell-directed MR contrast agents.

Massive culture of human liver cancer cells in a newly developed radial flow bioreactor system: ultrafine structure of functionally enhanced hepatocarcinoma cell lines

With a view to initiating clinical trials, cell morphology and function for a newly developed artificial liver support system employing highly functional human liver cell line, FLC-7, cultured in a radial flow bioreactor were compared to cells grown in a conventional monolayer culture. The radial flow bioreactor consists of a vertically extended cylindrical matrix comprised of porous glass bead microcarriers through which liquid medium flows from the periphery in toward the central axis generating a beneficial concentration gradient of oxygen and nutrients, while preventing excessive shear stresses or buildup of waste products. The three-dimensional culture system supports high-density (1.1 x 10(8) cells/ml-matrix), large scale cultures (4.4 x 10(10) cells/400 ml-bioreactor) with long-term viability. Scanning and transmission electron microscopy (SEM and TEM) revealed that cells cultured in a monolayer system were flattened and extended with numerous cytoplasmic projections. Cells in the three-dimensional culture were spherical and covered with microvillilike processes resembling liver cells in vivo. The cells were solidly attached on the surfaces and within the pores of the microcarriers in highly dense colonies. The spherical cells remained in close contact with adjacent cells, while circulation of liquid medium flowed freely through spaces between cells. FLC-7 cells produced albumin at a rate of 6.41 micrograms/24 h/10(6) cells. Alpha-fetoprotein (AFP) production dropped nearly threefold in comparison to monolayer cultures. Results demonstrated that the new artificial liver support systems (ALSS) provides a superior three-dimensional culture environment that allows cells to perform at naturally functioning levels.

Establishment and characterization of a nontumorigenic cell line derived from a human hepatocellular adenoma expressing hepatocyte-specific markers

In the present study the establishment and characterization of a nontumorigenic liver epithelial cell line (HACL-1) derived from a human hepatocellular adenoma is described. The HACL-1 cells have a finite life span (i.e., they proliferate for a period of 2 months and then senesce), show cell-cell contact inhibition, do not grow in soft agar, are not tumorigenic when injected in nude mice, and possess a normal diploid karyotype. The cultured cells resemble hepatocytes, but exhibit some features of dedifferentiation. At the ultrastructural level the cells are endowed with round or oval nuclei, abundant cytoplasmic organelles, and varying amounts of glycogen. The rough endoplasmic reticulum is disorganized, while peroxisomes and matrix granules within mitochondria are lacking. HACL-1 cells are cytokeratin 18-positive as well as (transiently) albumin- and alpha-fetoprotein-positive, but do not express cytokeratin 19. Furthermore, no mutations were observed in exons 5-8 of the tumor suppressor gene p53. Taken together these results show that HACL-1 cells are nontumorigenic proliferating liver epithelial cells, which might prove to be of great value in future studies on diverse aspects of human liver cell biology and carcinogenesis.