resulting in stabilized liver functions for several weeks in vitro. Studies have focused on using these models to investigate cell responses to drugs and other stimuli (for example, viruses and cell differentiation cues) to predict clinical outcomes. Gregory H. Underhill, PhD, from the department of bioengineering at the University of Illinois at Urbana-Champaign and Salman R. Khetani, PhD, from the department of bioengineering at the University of Illinois in Chicago presented a comprehensive review of the these advances in bioengineered liver models in Cellular and Molecular Gastroenterology and Hepatology (doi: 10.1016/j.jcmgh.2017.11.012).
Drug-induced liver injury (DILI) is a leading cause of drug attrition in the United States, with some marketed drugs causing cell necrosis, hepatitis, cholestasis, fibrosis, or a mixture of injury types. Although the Food and Drug Administration requires preclinical drug testing in animal models, differences in species-specific drug metabolism pathways and human genetics may result in inadequate identification of potential for human DILI. Some bioengineered liver models for in vitro studies are based on tissue engineering using high-throughput microarrays, protein micropatterning, microfluidics, specialized plates, biomaterial scaffolds, and bioprinting.
High-throughput cell microarrays enable systematic analysis of a large number of drugs or compounds at a relatively low cost. Several culture platforms have been developed using multiple sources of liver cells, including cancerous and immortalized cell lines. These platforms show enhanced capabilities to evaluate combinatorial effects of multiple signals with independent control of biochemical and biomechanical cues. For instance, a microchip platform for transducing 3-D liver cell cultures with genes for drug metabolism enzymes featuring 532 reaction vessels (micropillars and corresponding microwells) was able to provide information about certain enzyme combinations that led to drug toxicity in cells. The high-throughput cell microarrays are, however, primarily dependent on imaging-based readouts and have a limited ability to investigate cell responses to gradients of microenvironmental signals.
Liver development, physiology, and pathophysiology are dependent on homotypic and heterotypic interactions between parenchymal and nonparenchymal cells (NPCs). Cocultures with both liver- and nonliver-derived NPC types, in vitro, can induce liver functions transiently and have proven useful for investigating host responses to sepsis, mutagenesis, xenobiotic metabolism and toxicity, response to oxidative stress, lipid metabolism, and induction of the acute-phase response. Micropatterned cocultures (MPCCs) are designed to allow the use of different NPC types without significantly altering hepatocyte homotypic interactions. Cell-cell interactions can be precisely controlled to allow for stable functions for up to 4-6 weeks, whereas more randomly distributed cocultures have limited stability. Unlike randomly distributed cocultures, MPCCs can be infected with HBV, HCV, and malaria. Potential limitations of MPCCs include the requirement for specialized equipment and devices for patterning collagen for hepatocyte attachment.
