An in vitro model for peroxisome proliferation utilizing primary hepatocytes in sandwich culture

Peroxisome proliferators comprise a group of structurally diverse chemicals which share as a common biologic effect the induction of peroxisomal fatty acid degrading enzymes. Concomitantly, the number and size of peroxisomes within hepatocytes increases. Following chronic administration some peroxis ome proliferators act as non-genotoxic hepatocarcinogens in susceptible spe cies such as rodents. To establish an in vitro model for the toxicological investigation of peroxisome proliferation, primary hepatocytes of rats, dog s and humans were cultivated in an organotypic cell culture model (sandwich model). By employing a panel of diverse compounds in this model a graded r esponse was observed in the induction of carnitine acetyl transferase (CAT) , the activity of which was determined as an endpoint. The following result s were obtained in the order of decreasing inducing potential for rat hepat ocytes: FOE 3798 > nafenopin > fenofibrate (< clofibrate > ciprofibrate > b ezafibrate much greater than DEHP approximate to ETYA > DEHA. Induction of CAT activity was generally higher than reported in earlier cell culture sys tems, probably reflecting the effect of the extracellular matrix provided b y the collagen gel sandwich. In parallel, transcription of the rat CYP4A1 g ene was induced by a similar order of magnitude as measured by TaqMan RT-PC R. In accordance with literature data, human and dog hepatocytes did not di splay such a strong and graded response but rather were not susceptible to this effect. In addition, H-3-thymidine incorporation data demonstrated tha t nafenopin was able to induce DNA synthesis in rat hepatocytes whereas it did not in human hepatocytes. (C) 1999 Elsevier Science Ltd. All rights res erved.