Effects of Inducers of Drug Metabolism on Cytosolic Glutathione S-transferase Activity in Rat Hepatoma-derived Fa32 Cells

Paul J. Dierickx

Established Fa32 cells, derived from a rat hepatoma, were investigated for their glutathione S-transferase (GST) induction capacity, which is an important characteristic of the detoxification capacity in normal liver. The cells were exposed to inducers of drug metabolism for 3 days in complete medium (containing 10% fetal calf serum). Neither dimethyl sulphoxide nor dimethyl formamide could be used as a vehicle to transport the inducers into the cells, because they also interacted with GST. Phenobarbital, butylated hydroxyanisole, allyl isothiocyanate and dimethyl fumarate (but not fumaric acid) all effectively increased the total specific GST activity. None of the test chemicals produced a very pronounced induction of specific GST subunits, but subunit 2 and subunit 8 were increased more than the others. The effects of inducers of drug metabolism on the GST activity in Fa32 cells are comparable with those in rat liver. These cells can therefore be used as a valuable alternative model for GST-dependent metabolic interactions in rat liver.
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The Use of Long-term Hepatocyte Cultures for Detecting Induction of Drug Metabolising Enzymes: The Current Status

Sandra Coecke, Vera Rogiers, Martin Bayliss, José Castell, Johannes Doehmer, Gérard Fabre, Jeffrey Fry, Armin Kern and Carl Westmoreland

In this report, metabolically competent in vitro systems have been reviewed, in the context of drug metabolising enzyme induction. Based on the experience of the scientists involved, a thorough survey of the literature on metabolically competent long-term culture models was performed. Following this, a prevalidation proposal for the use of the collagen gel sandwich hepatocyte culture system for drug metabolising enzyme induction was designed, focusing on the induction of the cytochrome P450 enzymes as the principal enzymes of interest. The ultimate goal of this prevalidation proposal is to provide industry and academia with a metabolically competent in vitro alternative for long-term studies. In an initial phase, the prevalidation study will be limited to the investigation of induction. However, proposals for other long-term applications of these systems should be forwarded to the European Centre for the Validation of Alternative Methods for consideration. The prevalidation proposal deals with several issues, including: a) species; b) practical prevalidation methodology; c) enzyme inducers; and d) advantages of working with independent expert laboratories. Since it is preferable to include other alternative tests for drug metabolising enzyme induction, when such tests arise, it is recommended that they meet the same level of development as for the collagen gel sandwich long-term hepatocyte system. Those tests which do so should begin the prevalidation and validation process.
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