S5: Liver fibrosis: Corroboration and improvement
Liver fibrosis: Corroboration and improvement of the existing AOP using in vitro data
University of Applied Sciences Northwestern Switzerland (FHNW)
In the past few years, the concept of Adverse Outcome Pahway (AOP) has been generated to help develop testing strategies for relevant toxicities. An AOP is per definitio a linear sequence of events that commences with a Molecular Initiating Event, followed by a number of Key Events that ultimately lead to an adverse outcome at the tissue and organ level. Although several weaknesses of the use of AOPs have been discussed (e.g. their linearity), they have become useful tools for the evaluation of the specific toxicological phenomena that they describe. The generation of an AOP does not necessarily require an in depth knowledge of all cellular and molecular processes involved in each step. However, such mechanistic understanding adds to the weight of evidence and improves the quality of an AOP by increasing its plausibility.
One of the AOPs recently described and published concerns liver fibrosis. In this paper, I will present empirical data generated in vitro using a novel human, 3D-liver co-culture system that provides additional support to the described liver fibrosis AOP. The selected in vitro model comprises cell lines representing the three key cell types that are involved in the key cellular events associated with fibrosis: hepatocytes, Kupffer cells and stellate cells. The data generated in this 3D-system supports the involvement of hepatocyte damage, of release of pro-inflammatory cytokines by macrophages cells and activation of stellate cells leading to the increase production and deposition of ECM (e.g. collagen). Moreover, the model has allowed us to uncover additional factors that play a role on the proliferation of stellate cells as well as on the influence of oxidative stress on the activation of stellate cells.
In summary, the 3D-live co-culture model can reproduce the fibrotic phenotype and modulation of the system as a whole or of each independent cell type provides empirical information on the involved mechanisms.