Daniel Knobeloch

HepaRG human hepatic cell line utility as a surrogate for primary human hepatocytes in drug metabolism assessment in vitro.

INTRODUCTION Primary human hepatocytes are considered as a highly predictive in vitro model for preclinical drug metabolism studies. Due to the limited availability of human liver tissue for cell isolation, there is a need of alternative cell sources for pharmaceutical research. METHODS In this study, the metabolic activity and long-term stability of the human hepatoma cell line HepaRG were investigated in comparison to primary human hepatocytes (pHH). Hepatocyte-specific parameters (albumin and urea synthesis, galactose and sorbitol elimination) and the activity of human-relevant cytochrome P450 (CYP) enzymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) were assayed in both groups over a period of 14 days subsequently to a two week culture period in differentiated state in case of the HepaRG cells, and compared with those of cryopreserved hepatocytes in suspension. In addition, the inducibility of CYP enzymes and the intrinsic clearances of eleven reference drugs were determined. RESULTS The results show overall stable metabolic activity of HepaRG cells over the monitored time period. Higher albumin production and galactose/sorbitol elimination rates were observed compared with pHH, while urea production was not detected. CYP enzyme-dependent drug metabolic capacities were shown to be stable over the cultivation time in HepaRG cells and were comparable or even higher (CYP2C9, CYP2D6, CYP3A4) than in pHH, whereas commercially available hepatocytes showed a different pattern The intrinsic clearance rates of reference drugs and enzyme induction of most CYP enzymes were similar in HepaRG cells and pHH. CYP1A2 activity was highly inducible in HepaRG by β-naphthoflavone. DISCUSSION In conclusion, the results from this study indicate that HepaRG cells could provide a suitable alternative to pHH in pharmaceutical research and development for metabolism studies such as CYP induction or sub-chronic to chronic hepatotoxicity studies.

Profiling Induction of Cytochrome P450 Enzyme Activity by Statins Using a New Liquid Chromatography-Tandem Mass Spectrometry Cocktail Assay in Human Hepatocytes

Human hepatocytes in primary culture are a very useful model to directly assess induction of gene expression by xenobiotics. We developed a cytochrome P450 (P450) activity cocktail assay using model substrates for the seven important P450s 1A2 (phenacetin), 2B6 (bupropion), 2C8 (amodiaquine), 2C9 (tolbutamide), 2C19 (S-mephenytoin), 2D6 (propafenone), and 3A4 (atorvastatin). Metabolite formation was determined by liquid chromatography-tandem mass spectrometry in hepatocyte culture supernatants. Atorvastatin has not been previously assessed as a CYP3A probe drug. We demonstrate highly selective atorvastatin ortho-hydroxylation by CYP3A4 by recombinant P450s. In human liver microsomes ortho-hydroxyatorvastatin formation was highly correlated with CYP3A4 protein content (rs = 0.78, p < 0.0001, n = 150). We profiled induction of these P450 activities in primary human hepatocytes after treatment with 30 μM atorvastatin, lovastatin, pravastatin, rosuvastatin, and simvastatin for 24 to 72 h. Except for pravastatin, all statins induced P450 activities to various degrees, approximately in the order atorvastatin > simvastatin > lovastatin > rosuvastatin. Inducibility of P450s followed the order CYP2C8 > CYP3A4 > CYP2C9 > CYP2B6 > CYP2C19 ∼ CYP2D6 > CYP1A2. The strongest induction was observed for amodiaquine N-desalkylation, which was induced approximately 20-fold. Quantitative reverse transcription-polymerase chain reaction confirmed corresponding changes on the mRNA level with even more dramatic induction up to almost 100-fold. These data suggest a broader inducing effect of statins on cytochrome P450s and possibly other absorption, distribution, metabolism, and excretion genes than previously known, thus further emphasizing their drug-drug interaction potential. Our cocktail assay should be helpful for economical use of human hepatocytes in the assessment of P450 induction by drugs and drug candidates.

Analysis of drug metabolism activities in a miniaturized liver cell bioreactor for use in pharmacological studies.

Based on a hollow fiber perfusion technology with internal oxygenation, a miniaturized bioreactor with a volume of 0.5 mL for in vitro studies was recently developed. Here, the suitability of this novel culture system for pharmacological studies was investigated, focusing on the model drug diclofenac. Primary human liver cells were cultivated in bioreactors and in conventional monolayer cultures in parallel over 10 days. From day 3 on, diclofenac was continuously applied at a therapeutic concentration (6.4 µM) for analysis of its metabolism. In addition, the activity and gene expression of the cytochrome P450 (CYP) isoforms CYP1A2, CYP2B6, CYP2C9, CYP2D6, and CYP3A4 were assessed. Diclofenac was metabolized in bioreactor cultures with an initial conversion rate of 230 ± 57 pmol/h/106 cells followed by a period of stable conversion of about 100 pmol/h/106 cells. All CYP activities tested were maintained until day 10 of bioreactor culture. The expression of corresponding mRNAs correlated well with the degree of preservation. Immunohistochemical characterization showed the formation of neo‐tissue with expression of CYP2C9 and CYP3A4 and the drug transporters breast cancer resistance protein (BCRP) and multidrug resistance protein 2 (MRP2) in the bioreactor. In contrast, monolayer cultures showed a rapid decline of diclofenac conversion and cells had largely lost activity and mRNA expression of the assessed CYP isoforms at the end of the culture period. In conclusion, diclofenac metabolism, CYP activities and gene expression levels were considerably more stable in bioreactor cultures, making the novel bioreactor a useful tool for pharmacological or toxicological investigations requiring a highly physiological in vitro representation of the liver. Biotechnol. Bioeng. 2012; 109: 3172–3181.

Human hepatocytes: isolation, culture, and quality procedures.

The use of isolated human liver cells in research and development has gained increasing interest during the past years. The possible application may vary between elucidation of new biochemical pathways in liver diseases, drug development, safety issues, and new therapeutic strategies up to direct clinical translation for liver support. However, the isolation of human liver cells requires a well-developed logistic network among surgeons, biologists, and technicians to obtain a high quality of cells. Our laboratories have been involved in various applications of human liver cells and we have long-lasting experiences in human liver cell isolation and their application in R&D. We here summarize the present protocol of our laboratories for cell isolation from normal resected liver tissue, the most common tissue available. In addition, we discuss the necessary network in the clinic and quality controls to maintain human liver cells in culture and the effect of 3D extracellular matrix in cultured cells which results in preservation of hepatocyte epithelial polarity in the form of bile canaliculi and repression of epithelial to mesenchymal transitions occurring in 2D cultures.

In‐depth physiological characterization of primary human hepatocytes in a 3D hollow‐fiber bioreactor

As the major research focus is shifting to three‐dimensional (3D) cultivation techniques, hollow‐fiber bioreactors, allowing the formation of tissue‐like structures, show immense potential as they permit controlled in vitro cultivation while supporting the in vivo environment. In this study we carried out a systematic and detailed physiological characterization of human liver cells in a 3D hollow‐fiber bioreactor system continuously run for > 2 weeks. Primary human hepatocytes were maintained viable and functional over the whole period of cultivation. Both general cellular functions, e.g. oxygen uptake, amino acid metabolism and substrate consumption, and liver‐specific functions, such as drug‐metabolizing capacities and the production of liver‐specific metabolites were found to be stable for > 2 weeks. As expected, donor‐to‐donor variability was observed in liver‐specific functions, namely urea and albumin production. Moreover, we show the maintenance of primary human hepatocytes in serum‐free conditions in this set‐up. The stable basal cytochrome P450 activity 3 weeks after isolation of the cells demonstrates the potential of such a system for pharmacological applications. Liver cells in the presented 3D bioreactor system could eventually be used not only for long‐term metabolic and toxicity studies but also for chronic repeated dose toxicity assessment. Copyright

Serum-free culture of primary human hepatocytes in a miniaturized hollow-fibre membrane bioreactor for pharmacological in vitro studies.

Primary human hepatocytes represent an important cell source for in vitro investigation of hepatic drug metabolism and disposition. In this study, a multi‐compartment capillary membrane‐based bioreactor technology for three‐dimensional (3D) perfusion culture was further developed and miniaturized to a volume of less than 0.5 ml to reduce demand for cells. The miniaturized bioreactor was composed of two capillary layers, each made of alternately arranged oxygen and medium capillaries serving as a 3D culture for the cells. Metabolic activity and stability of primary human hepatocytes was studied in this bioreactor in the presence of 2.5% fetal calf serum (FCS) under serum‐free conditions over a culture period of 10 days. The miniaturized bioreactor showed functions comparable to previously reported data for larger variants. Glucose and lactate metabolism, urea production, albumin synthesis and release of intracellular enzymes (AST, ALT, GLDH) showed no significant differences between serum‐free and serum‐supplemented bioreactors. Activities of human‐relevant cytochrome P450 (CYP) isoenzymes (CYP1A2, CYP3A4/5, CYP2C9, CYP2D6, CYP2B6) analyzed by determination of product formation rates from selective probe substrates were also comparable in both groups. Gene expression analysis showed moderately higher expression in the majority of CYP enzymes, transport proteins and enzymes of Phase II metabolism in the serum‐free bioreactors compared to those maintained with FCS. In conclusion, the miniaturized bioreactor maintained stable function over the investigated period and thus provides a suitable system for pharmacological studies on primary human hepatocytes under defined serum‐free conditions. Copyright

NeoHepatocytes From Alcoholics and Controls Express Hepatocyte Markers and Display Reduced Fibrogenic TGF‐β/Smad3 Signaling: Advantage for Cell Transplantation?

BACKGROUND Liver transplantation is the only definitive treatment for end stage liver disease. Donor organ scarcity raises a growing interest in new therapeutic options. Recently, we have shown that injection of monocyte-derived NeoHepatocytes can increase survival in rats with extended liver resection. In order to apply this technology in humans with chronic liver diseases in an autologous setting, we generated NeoHepatocytes from patients with alcoholic liver disease and healthy controls and compared those to human hepatocytes. METHODS We generated NeoHepatocytes from alcoholics with Child A and B cirrhosis and healthy controls. Hepatocytes marker expression and transforming growth factor (TGF)-beta signaling was investigated by RT-PCR, Western blot, immunofluorescent staining, and adenoviral reporter assays. Glucose and urea was measured photometrically. Phase I and II enzyme activities were measured using fluorogenic substrates. Neutral lipids were visualized by Oil Red O staining. RESULTS There was no significant difference in generation and yield of NeoHepatocytes from alcoholics and controls. Hepatocyte markers, e.g., cytokeratin18 and alcohol dehydrogenase 1, increased significantly throughout differentiation. Glucose and urea production did not differ between alcoholics and controls and was comparable to human hepatocytes. During differentiation, phase I and II enzyme activities increased, however remained significantly lower than in human hepatocytes. Fat accumulation was induced by treatment with insulin, TGF-beta and ethanol only in differentiated cells and hepatocytes. TGF-beta signaling, via Smad transcription factors, critically required for progression of chronic liver disease, was comparable among the investigated cell types, merely expression of Smad1 and -3 was reduced (approximately 30 and approximately 60%) in monocytes, programmable cells of monocytic origin, and NeoHepatocytes. Subsequently, expression of TGF-beta regulated pro-fibrogenic genes, e.g., connective tissue growth factor and fibronectin was reduced. CONCLUSIONS Generation of NeoHepatocytes from alcoholics, displaying several features of human hepatocytes, offers new perspectives for cell therapeutic approaches, as cells can be obtained repeatedly in a noninvasive manner. Furthermore, the autologous setting reduces the need for immunosuppressants, which may support recovery of patients which are declined for liver transplantation.

Hepatotropic growth factors protect hepatocytes during inflammation by upregulation of antioxidative systems

AIM To investigate effects of hepatotropic growth factors on radical production in rat hepatocytes during sepsis. METHODS Rat hepatocytes, isolated by collagenase perfusion, were incubated with a lipopolysaccharide (LPS)-containing cytokine mixture of interleukin-1β, tumor necrosis factor-α and interferon-γ to simulate sepsis and either co-incubated or pre-incubated with hepatotropic growth factors, e.g. hepatocyte growth factor, epidermal growth factor and/or transforming growth factor-α. Cells were analyzed for glutathione levels. Culture supernatants were assayed for production of reactive oxygen intermediates (ROIs) as well as NO(2) (-), NO(3) (-) and S-nitrosothiols. To determine cellular damage, release of aspartate aminotransferase (AST) into the culture medium was analyzed. Activation of nuclear factor (NF)-κB was measured by electrophoretic mobility shift assay. RESULTS Rat hepatocytes treated with the LPS-containing cytokine mixture showed a significant increase in ROI and nitrogen oxide intermediate formation. AST leakage was not significantly increased in cells treated with the LPS-containing cytokine mixture, independent of growth-factor co-stimulation. However, pretreatment with growth factors significantly reduced AST leakage and ROI formation while increasing cellular glutathione. Application of growth factors did not result in increased NF-κB activation. Pretreatment with growth factors further increased formation of NO(2) (-), NO(3) (-) and S-nitrosothiols in hepatocytes stimulated with LPS-containing cytokine mixture. Thus, we propose that, together with an increase in glutathione increased NO(2) (-), NO(3) (-) formation might shift their metabolism towards non-toxic products. CONCLUSION Our data suggest that hepatotropic growth factors positively influence sepsis-induced hepatocellular injury by reducing cytotoxic ROI formation via induction of the cellular protective antioxidative systems.

Further characterization of autologous NeoHepatocytes for in vitro toxicity testing

Gold standard for in vitro toxicity tests and drug screenings is primary human hepatocytes (hHeps). Because of their limited availability efforts have been made to provide alternatives, e.g., monocyte-derived NeoHepatocytes. In the past years it has been critically discussed if gaining hepatocyte features is associated with trans-differentiation of monocytes or their activation towards a macrophage phenotype. Generating NeoHepatocytes in the presence of six different human AB sera, fetal calf serum (FCS) or autologous serum showed that yield and quality of NeoHepatocytes is inversely correlated to macrophage activation. Using autologous serum constantly the highest amount of cells with the best metabolic capacity was obtained. Focus of this study was to further analyze bio-transformation capacity of the optimized NeoHepatocytes for use as in vitro toxicity test-system. Treatment of the optimized NeoHepatocytes with two different pro-teratogenic substances with corresponding metabolites and eight known hepatotoxins showed comparable toxicity to hHeps. Bio-transformation rates, assessed by testosterone metabolism, were comparable in both cell types. Our data reveal that use of autologous serum reduced macrophage activation which improved yield and function of NeoHepatocytes resulting in bio-transformation and toxicity profiles comparable to hHeps. Thus, their easy accessibility makes them an ideal candidate for in vitro toxicity studies.