Multicellular liver systems and how to deconvolute toxicity in a complex system?

The liver is a major site for xenobiotic-induced toxicity and in vitro systems often focus on the hepatocyte. However, multicellular 3D-systems are better suited to reflect some types of toxicities such as immune-mediated responses and liver fibrosis. Immune-mediated liver toxicity may involve Kupffer cells or Hepatic sinusoidal cells (LSECs). Liver fibrosis involves a series of key events described in the adverse outcome pathway (AOP) #38, based on the interaction of at least three cellular players: hepatocytes, Kupffer cells, and hepatic stellate cells. Hence, complex in vitro systems are required to assess these effects. For example, 3D-co-culture spheroid models can reproduce a fibrotic phenotype and mimic the key events characteristic of the liver fibrosis AOP (hepatocellular damage, activation of Kupffer cells, activation of stellate cells and deposition of extracellular matrix). However, in these complex systems it is difficult to understand the contribution of each cell type to the observed response. Studies implementing co-cultures, monocultures, and cell-type specific endpoints such as cellular respiration and release of miRNAs can help better discern the specific involvement of target cells. As specific examples, we evaluated the effects of methotrexate and the response to adeno-associated viruses (AAVs) of several liver cell types.