| Abstract |
The scope of conventional cytotoxicity tests does not usually include various metabolic processes in humans. We therefore developed a physiologically based multicompartment perfusion coculture system (biohybrid simulator) using a Caco-2 cell monolayer on a semipermeable membrane and a microcarrier-based three-dimensional culture of Hep G2 cells to mimic absorption across the small intestine and biotransformation in the small intestine and the liver. Stable operation enabled the maintenance of various activities of both cell types for at least 4 days. Cocultivation improved the growth of Hep G2 cells and enhanced the cytochrome P450 1A1/2 capacities of both cell lines. When benzo[a]pyrene (BaP) was introduced to the apical side of the Caco-2 cell layer, the enhanced P450 capacities produced a larger amount of BaP-7,8-hydrodiol, an immediate precursor to the highly reactive ultimate toxicant of BaP, BaP-7,8-dihydrodiol-9,10-epoxide. This led to initially retarded and later stronger expression of BaP toxicity in the coculture system than in pure culture, which agreed well with the largest time integral of the concentration (area under curve) of BaP-7,8-hydrodiol in the Hep G2 cell compartment of the coculture system. Because this kind of system can reproduce such complicated phenomena, including those derived from organ-to-organ interactions, it is useful as a new in vitro experimental system to help elucidate unknown mechanisms involved in final toxicity in humans and to develop physiologically based pharmacokinetic numerical simulation models.
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