In vitro models

Due to its major role in xenobiotic metabolism (i.e. drugs), the liver is a target for many chemical toxicants. Drug-induced liver disease represents a major economic challenge for the pharmaceutical industry since as many as 1/3 of new drugs fail due to interactions with the liver. Whole animal models provide a limited view of human toxicity due to species variations as well as animal-to-animal variability. Incorporating in vitro liver models into drug development provide several advantages: earlier elimination of potentially toxic drugs, reduction in variability by allowing hundreds of experiments per animal, and human liver models without patient exposure. However, most current in vitro liver models typically lack long-term phenotypic hepatocyte stability and do not represent zones of liver where many drugs exhibit selective toxicity. Thus, chronic and zonal effects of xenobiotics on liver are difficult to examine in vitro. To address these limitations, we are using novel microfabrication tools to develop a long-term (weeks to months), stable model of liver tissue in vitro by co-cultivating primary hepatocytes with nonparenchymal cells. Our co-cultures demonstrate long-term activity of major detoxification enzymes (i.e. CYP450) and can be easily characterized using conventional microscopy. Also, we have shown that exposure of co-cultures to physiologic gradients of dissolved oxygen in a parallel plate bioreactor induces zonated functions (see soluble stimuli ) and susceptibility to a zonal toxin, acetaminophen (APAP). As can be seen in the figure below, greatest cell death (lowest relative optical density) occurred in regions of low oxygen tensions (outlet). In addition to drug screening applications, such in vitro toxicological tests may provide insight into the mechanism of drug metabolism and toxicity in vivo. Allen et al, 2005.

Zonal Toxicity of Hepatocytes In Vitro. Lack of purple viability staining indicates downstream cell death in response to acetaminophen exposure.