Concurrent administration of ascorbic acid tumor - promoting activity of kojic acienhances 1 d in rats iver

We previously fbund that administration ofascorbic ac{d (AA) enhances thc liver tumorpromoting activity ofkojic acid (KA) in rnice. To examine the reproducibility ofthese results in rats and thc underlying inechanism of this effbct, we ernployed a two-stage liver carcinogenesis model using male F344 rats. Two weeks after initiation with diethylnitrosamine (DEN), the animals received a diet containing 2% KA and drinking water with or without 5,OOO ppm AA fbr a period of 7 weeks. A DENalone group was also established as a control. One week after the commenccment of thc administration, the animals wcre subjected to two-thirds partial hepatectomy. At the end of the experiment, the livers werc analyzed immunohistochemically, and the mRNA expression level and extent of lipid peroxidation were measured. AA treatment enhanced the KA-induced tumor-promoting activity in terrns of the number and area ofliver cell fbci that were positive for glutathione-S-transferase p]acental fbrm, AA coadministration increased the number ofhepatocytes positive fbr proliferating cell nuclear antigen and inversely decreased the numbcr ofTUNEL-positive cells. However, the increased leyel ofthiobarbituric acid reactive substances resu[ting from KA treatment was suppressed by coadministration ofAA. Gene expression analyses using low-density microarrays and real-tirRe FULPCR showed that coadministration ofAA resulted in upregulation of genes related to cell proliferation and downregulation of those involved in apoptosis andfor cell cycle arrest. Thes¢ resu]ts indicate that the concerted effects ofAA on cell proliferation and apoptosis/cell cycle arrest probably through its antioxidant activity are involved in this enhancement.