抄録
Usual cytotoxicity tests do not include various metabolic processes such as absorption from the small intestine or biotransformation in the liver and small intestine in humans. We therefore developed a physiologically based perfusion coculture system using a Caco-2 and Hep G2 cells; the former was used as a representative of the small intestinal membrane and the latter was used as the liver tissue. Such perfusion cocultivation enhanced the growth of Hep G2 cells and the cytochrome P450 1A1/2 capacities of both cell lines. When benzo[a]pyrene (BaP) was introduced as a model toxicant 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. Although such BaP metabolites were preferably secreted back into the apical side of the Caco-2 membrane, the enhanced production of BaP-7,8-hydrodiol led to initially retarded and later stronger expression of BaP toxicity in the coculture system than in pure culture. This kinetics of the toxicity agreed well with the largest time integral of the concentration of BaP-7,8-hydrodiol in the Hep G2 cell compartment. Because this system can reproduce such complicated phenomena in vitro, including those derived from organ-to-organ interactions, it is useful as a new cytotoxicity test to help elucidate unknown mechanisms and to develop physiologically based pharmacokinetic numerical simulation models.
