USE OF ORGANOTYPICAL CULTURES OF PRIMARY HEPATOCYTES TO ANALYZE DRUG BIOTRANSFORMATION IN MAN AND ANIMALS

1. In conventional single-gel culture systems for primary hepatocytes, rapid loss of drug metabolizing capacities is a common feature and parallels general loss of function. An organotypical (double gel) culture technique for primary hepatocytes is established by enclosing the cells within two layers of extra cellular matrix. This serves to imitate thk in vivo microenvironment within the space of Disse. Using rat hepatocytes, this technique has been shown previously to maintain protein synthetic functions in vitro and to allow more efficient P450A-dependent biotransformation of drugs than a standard single-gel culture system. 2. The aim was to test the capacity of this organotypical culture model for primary rat and human hepatocytes to generate drug metabolites in a typical species-dependent pattern. 3. Urapidil, an antihypertensive drug, was used as a test compound, since it is metabolized in vivo in a species-dependent manner in rat and man. 4. Primary rat and human hepatocytes were cultured within two layers of collagen and exposed to 2.25 mu g/ml urapidil for periods of 1-24h at 3 days in culture. Urapidil metabolites were measured using hplc. 5. Metabolite M1 (hydroxylated product) was produced preferentially in human hepatocyte cultures, and metabolites M2/M3 (O-demethylated, N-demethylated product) were preferentially generated in rat cultures. This corresponded to the in vivo pattern found in man and rat, respectively. 6. Since in vitro urapidil metabolism by human and rat hepatocytes cultured in a double-gel system reflects that in vivo, it is suggested that information from such a system may be useful to predict the metabolic pathway of novel xenobiotics and to direct further toxicological evaluation.