Combining cell culture analogue reactor designs and PBPK models to probe mechanisms of naphthalene toxicity

An alternative method of evaluating the toxicology of a chemical is to use cultured mammalian cells in a novel cell culture analogue reactor (CCA) tog ether with a corresponding physiologically based pharmacokinetic model (PBP K). The PBPK is a mathematical model that divides the body into compartment s representing organs, integrating the kinetic, thermodynamic, and anatomic al parameters of the animal. The bioreactor is a physical replica of the PB PK; where the PBPK specifies an organ or tissue compartment, the bioreactor contains compartments with a corresponding cell type. The device is a cont inuous, dynamic system composed of multiple cell types that interact throug h a common circulating cell culture medium. The bioreactor and the model ar e coupled to evaluate the plausibility of the molecular mechanism that is i nput into the model. This concept is tested with naphthalene as a model of PAH (polycyclic aromatic hydrocarbons) toxicants. Two physically different CCA reactors were tested with naphthalene, and different results were obser ved. In the prototype system using cells attached to glass dilution bottles , naphthalene dosing resulted in generation of a circulating metabolite fro m the "liver" compartment (based on H4IIE cells from a rat hepatoma) that c aused cell death in the "lung" compartment (L2 cells from a rat lung), as w ell as depletion of glutathione in the L2 cells. An improved CCA using pack ed bed reactors of microcarrier cultured cells did not show differences bet ween naphthalene-dosed and nondosed controls. To explain the different resp onses of the two CCA designs, PBPKs of the two reactors were tested with va riations in physical and kinetic parameters, and toxic mechanism. When the toxic metabolite of naphthalene was naphthoquinone rather than naphthalene epoxide as initially assumed, the PBPK results were consistent with the res ults of the two CCA designs. This result indicates that the mechanism of na phthalene toxicity in the CCAs may be mediated through naphthoquinone forma tion. The CCA-PBPK concept is demonstrated to be applicable to the study of toxic mechanisms. In particular, use of this approach suggests that in vit ro naphthalene toxicity is mediated through the naphthoquinone metabolite.