LACK OF EFFECT OF COUMARIN ON UNSCHEDULED DNA-SYNTHESIS IN PRECISION-CUT HUMAN LIVER SLICES

In this study the effect of coumarin on unscheduled DNA synthesis (UDS ) in precision-cut human liver slices has been examined. Liver slices from tissue samples from four donors were cultured for 24 hr in medium containing [H-3]thymidine and 0-5.0 mM coumarin using a dynamic organ culture system and processed for autoradiographic evaluation of UDS. As positive controls liver slices were also cultured with three known genotoxic agents, namely 0.02 and 0.05 mM 2-acetylaminofluorene (2-AAF ), 0.002 and 0.02 mM aflatoxin B-1 (AFB(1)) and 0.005 and 0.05 mM 2-am ino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). UDS was quantified as the net grain count in centrilobular hepatocytes and as the percen tage of centrilobular hepatocyte nuclei with more than five net grains . Compared with control liver slice cultures, treatment with 0.05-5.0 mM coumarin had no effect on UDS. In contrast, treatment with 0.02 and 0.05 mM 2-AAF, 0.002 and 0.02 mM AFB(1) and 0.005 and 0.05 mM PhIP pr oduced significant increases in the net grain counts of centrilobular hepatocytes. The greatest induction of UDS was observed in liver slice s treated with 0.05 mM PhIP. Treatment with 2-AAF, AFB(1) and PhIP als o produced significant increases in the number of centrilobular hepato cyte nuclei with more than five net grains. At the concentrations exam ined neither coumarin, 2-AAF, AFB1 nor PhIP had any significant effect on replicative DNA synthesis in 24 hr cultured human liver slices. Th ese results demonstrate that coumarin does not induce UDS in cultured human liver slices. However, all three positive control compounds prod uced marked significant increases in UDS, thus confirming the function al viability of the human liver slice preparations used in this study. The results of this study suggest that coumarin is not a genotoxic ag ent in human liver. (C) 1998 Elsevier Science Ltd. All rights reserved