(660e) Microfluidic Gradient Chamber for Two-Dimensional Mapping of Hepatic Drug Response

A major concern in drug development is the potential for chemical injury to the liver, which is the major site of xenobiotic transformation in the body. Drugs have been estimated to account for 1/3 to 1/2 of acute liver failures. Unfortunately, adverse drug reactions (ADRs) are usually not detected during drug development. In this paper, we present a microfluidic gradient device for in vitro studies on hepatocyte drug metabolism. Two key novel features of this device are that the design affords long-term culture and steady diffusion gradients of various shapes across the cell compartment. Numerical solutions to coupled cell growth and nutrient transport equations showed that the culture device supported medium flow rates sufficiently high for near-uniform axial profiles of oxygen and glucose. Experiments with a human hepatocellular carcinoma cell line HepG2 showed continued proliferation throughout the length of the culture compartment, in good agreement with the simulation results. Steady chemical gradients were established by fabricating a series of posts between the cell compartment and the medium channels. In one design, the post size and spacing was symmetrical about the culture compartment. In the second design, the posts on the left and right hand sides of the cell compartment differed in width. Using these two designs, linear and non-linear drug diffusion gradients were established across the cell culture chamber evoking different cell responses. The test drug was Troglitazone (TGZ), a thiazolidine dione compound that had previously used to treat type 2 diabetes, but has been withdrawn due to multiple incidences of severe hepatotoxicity. Nutrient gradients were established in conjunction with drug gradients, and their effect on hepatic function and drug hepatoxicity were examined. Cell function and health was monitored through fluorescent assays and study of the effluent medium from the microreactor. Our results suggest that the gradient culture device should enable efficient screening of hepatocyte drug responses in physiological micro-environments subjected to defined nutrient and hormonal gradients.