This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell–derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.Electronic supplementary materialThe online version of this article (doi:10.1007/s00204-013-1078-5) contains supplementary material, which is available to authorized users.

The three monokines interleukin-lg (IL-IS), tumor necrosis factor a (TNFa), and interleukind (IL-6) modulate acute phase plasma protein synthesis in adult human hepatocytes. Only IL-6 stimulates the synthesis of the full spectrum of acute phase proteins as seen in inflammatory states in humans, i.e. synthesis and secretion of C-reactive protein, serum amyloid A, fibrinogen, ar-antitrypsin, q-antichymotrypsin and haptoglobin are increased while albumin, transferrin and fibronectin are decreased. IL-lb as well as TNFa, although having a moderate effect on the positive acute phase proteins and inhibiting the synthesis of fibrinogen, albumin and transferrin, fail to induce serum amyloid A and C-reactive protein.These data suggest that IL-6 plays the key role in the regulation of acute phase protein synthesis in human hepatocytes.Acute phase protein; Interleukind; Interleukin-l/I; Tumor necrosis factor a; (Human hepatocyte)

Human hepatocytes in primary culture were used as a model system to investigate the mechanism(s) involved in the induction of the acute-phase response in human liver. Hepatocytes were incubated with increasing amounts of recombinant human interleukin-1 beta, recombinant interleukin-6 and tumor necrosis factor-alpha. Synthesis of C-reactive protein was studied at the mRNA and protein levels. Only recombinant interleukin-6 was capable of inducing C-reactive protein-mRNA and C-reactive protein-protein synthesis. Also, fibrinogen and alpha-1-antitrypsin synthesis measured by immunoprecipitation with specific antisera increased in a dose-dependent, time-dependent manner, whereas albumin synthesis decreased to about 50% of controls. Maximal effects were observed at 100 to 300 units of recombinant interleukin-6/ml culture medium after 20 hr of incubation. Although the synthetic glucocorticoid dexamethasone slightly modulated the effect of recombinant interleukin-6, it was not an absolute requirement for the induction of acute-phase protein synthesis in human hepatocytes. In pulse-chase experiments it was shown that the time course of the disappearance of the acute-phase proteins from the cells and their appearance in the medium is not influenced by recombinant interleukin-6. This finding suggests that recombinant interleukin-6 exerts its regulatory effect on acute-phase protein synthesis at the pretranslational level.

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