Comparative effects of clofibrate on peroxisomal enzymes of human (Hep EBNA2) and rat (FaO) hepatoma cell lines.

We compared the responses of the human Hep EBNA2 and rat FaO hepatoma lines to the peroxisome proliferator, clofibrate. Using spectrophotometrical assays performed with peroxisome-enriched fractions, the dose- and time-dependent increase of catalase and acyl-CoA oxidase activities were determined. For catalase activity a maximum stimulation of 1.2-fold for Hep EBNA2 and 1.7-fold for FaO lines was obtained. This increase was neither dose- nor time-dependent. The activity of the initial enzyme of the peroxisomal beta-oxidation system, acyl-CoA oxidase, was tested using two different biochemical assays. The maximum stimulation of acyl-CoA oxidase was 2.4 to 3-fold for human Hep EBNA2 and 6 to 11-fold for rat FaO lines. The specific activity of acyl-CoA oxidase increased with the concentration of clofibrate and with the length of the treatment. Dot blot analyses carried out using mRNAs from FaO and Hep EBNA2 cells treated with 0.5 mM clofibrate for 5 days and from control cells, confirmed the increase in the level of acyl-CoA oxidase mRNAs from the clofibrate-treated cells. In the human cell line, the level of mRNA encoding for the peroxisomal bifunctional enzyme which is involved in the second and the third step of the beta-oxidation system, was also increased by clofibrate treatment.