Liver Cell Models in in Vitro Toxicology

Abstract

In vitro liver preparations are increasingly used for the study of hepatotoxicity of chemicals. In recent years their actual advantages and limitations have been better defined. The cell models, slices, and mainly primary hepatocyte cultures, appear to be the most powerful in vitro systems, as liver-specific functions and responsiveness to inducers are retained either for a few days or several weeks depending on culture conditions. Maintenance of phase I and phase II xenobiotic metabolizing enzyme activities allows various chemical investigations to be performed, including determination of kinetic parameters, metabolic profile, interspecies comparison, inhibition and induction effects, and drug-drug interactions. In vitro liver cell models also have various applications in toxicology: screening of cytotoxic and genotoxic compounds, evaluation of chemoprotective agents, and determination of characteristic liver lesions and associated biochemical mechanisms induced by toxic compounds. Extrapolation of the results to the in vivo situation remains a matter of debate. Presently, the most convincing applications of liver cell models are the studies on different aspects of metabolism and mechanisms of toxicity. For the future, there is a need for better culture conditions and differentiated hepatocyte cell lines to overcome the limited availability of human liver tissues. In addition, strategies for in vitro analysis of potentially toxic chemicals must be better defined.

Changes in cytochrome P450 gene expression and enzyme activity induced by xenobiotics in rabbits in vivo and in vitro

“…Animal models are the gold standard but ethical and cost considerations favour in vitro systems such as primary hepatocyte cell cultures, which closely approximate to parent cells and provide high initial CYP450 activity (Guillouzo, 1998). A highly sensitive luminescence assay has been developed for assaying the human cytochrome system (Cali et al, 2006), and is specific for CYP isoenzyme activity.…”

Hepatotoxicity assay using human hepatocytes trapped in microholes of a microfluidic device

“…However, the hepatoma cell lines have lost various drug-metabolizing enzyme activities and genotype stability decreases over time [3]. Compared with primary human hepatocytes, moreover, the hepatoma cell lines have different properties with regard to the expression of cytochrome P450 and cytotoxic effect on cells.…”

“…The live cell fraction gradually decreased with time and increasing concentrations of drugs. The drug concentrations used were taken from conventional hepatotoxicity assays [2,3]. In the control experiment, the live cell fraction of suspended hepatocytes decreased because the cells were affected by microfluidic shear stress at the start of the assay, but this was constant after 2 h. Acetaminophen is one of the most widely used antipyretic and analgesic drugs, but it can cause severe hepatic failure upon overdose [25,26].…”

“…Suspended cryopreserved hepatocytes are a convenient cell source for toxicity studies because they have no lag-time between isolation from organs and starting experiments, in comparison with monolayer cultures that need an attachment period of at least several hours [1,3,5,[11][12][13]. However, suspended hepatocytes can only be used for short-term metabolism or cytotoxicity studies because such hepatocytes in suspension have a limited life-span, and lose their morphology and liver-specific functions after a short period of culture time [11,14].…”

“…Understanding biochemical mechanisms and functions of the liver is a key factor in drug discovery. Primary human hepatocytes are the major cell type comprising 80% of the liver, and they are widely used in investigating drug metabolism, the induction of drugmetabolizing enzymes, and cytotoxicity studies of drug candidates [1][2][3]5]. Consequently, cytotoxicity assays using primary human hepatocytes have accelerated drug development [6].…”