Abstract
Drug-induced liver injury (DILI) is the major reason for failures in drug development and withdrawal of approved drugs from the market. Two-dimensional cultures of hepatocytes often fail to reliably predict DILI: hepatoma cell lines such as HepG2 do not reflect important primary-like hepatic properties and primary human hepatocytes (pHHs) dedifferentiate quickly in vitro and are, therefore, not suitable for long-term toxicity studies. More predictive liver in vitro models are urgently required in drug development and compound safety evaluation. This review discusses available human hepatic cell types for in vitro toxicology analysis and their usage in established and emerging three-dimensional (3D) culture systems. Generally, 3D cultures maintain or improve primary hepatic functions (including expression of drug-metabolizing enzymes) of different liver cells for several weeks of culture, thus allowing long-term and repeated-dose toxicity studies. Spheroid cultures of pHHs have been comprehensively tested, but also other cell types such as HepaRG benefit from 3D culture systems. Emerging 3D culture techniques include usage of induced pluripotent stem-cell-derived hepatocytes and primary-like upcyte cells, as well as advanced culture techniques such as microfluidic liver-on-a-chip models. In-depth characterization of existing and emerging 3D hepatocyte technologies is indispensable for successful implementation of such systems in toxicological analysis.
Highlights
Any organotypic in vitro model becomes obsolete if it does not represent the unique characteristics of the tissue of origin in the focus of the research
The downregulation of hepatic properties already begins within 30 min of classical monolayer culture; within hours, crucial features such as the expression of albumin and cytochrome P450 (CYP) enzymes are almost lost, and typical hepatic morphology is deteriorated from day 2–3 onward
The results indicate that expression levels of CYP2C19, CYP3A4, MRP2 and OATP-C in spheroids were slightly higher than in 2D cultures, while CYP2C8 and BSEP expression was reduced in 3D cultures [41]
Summary
Any organotypic in vitro model becomes obsolete if it does not represent the unique characteristics of the tissue of origin in the focus of the research. In the field of toxicological studies on liver cells, it is a prerequisite that hepatocytes cultured in vitro display features of their in vivo counterparts. This is a major challenge, as primary hepatocytes dedifferentiate very quickly after isolation and culture. Cells and/or culture conditions must be used for standardized long-term (chronic) in vitro research on the effects of toxic compounds. Such long-term analyses of potentially liver-toxic substances are indispensable in drug development. Three-dimensional culture techniques of hepatocytes generally aim to maintain and/or improve primary hepatic properties and, provide well-accepted, and promising tools for application in toxicology analyses
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