Enhancement of hepatocarcinogenesis by kojic acid in rat two-stage models after initiation with N-bis(2-hydroxypropyl) nitrosamine or N-diethylnitrosamine

Kojic acid (KA) has been used as a food additive for preventing enzymatic browning of crustaceans and as a cosmetic agent for skin whitening. In the present experiments, effects of KA on the induction of hepatic pre-neoplastic lesions in N-bis(2-hydroxypropyl)nitrosamine-initiated (experiment 1) and non-initiated (experiment 2) models, and its promoting influence in a medium-term liver bioassay (experiment 3) were investigated at dietary doses of up to 2% in male F344 rats. In experiment 1, 2% KA feeding induced significant increases in numbers (22.3+/-13.0 vs 8.5+/-3.4 in the 0%) and areas (0.37+/-0.29 vs 0.05+/-0.03 in the 0%) of glutathione-S-transferase P form (GST-P)-positive foci and toxic changes such as vacuolation of hepatocytes and microgranulomas. The development of GST-P-positive foci was pronounced in the animals with hepatocellular toxic changes. In experiment 2, numbers (0.65+/-0.57 vs 0.17+/-0.28 in the 0%) and areas (0.005+/-0.005 vs 0.0007+/-0.0012 in the 0%) of GST-P-positive foci and hepatocellular proliferating cell nuclear antigen (PCNA) expression (3.8+/-2.3 vs 2.6+/-0.7 in the 0%) were significantly increased by the 2% treatment. The PCNA-positive hepatocytes were abundantly localized around the vacuolated and granulomatous legions in both experiments 1 and 2. In experiment 3, significant increases in numbers (16.9+/-3.2 vs 8.4+/-2.7 in the 0%) and areas (1.62+/-0.39 vs 0.77+/-0.34 in the 0%) of GST-P-positive foci were again observed with 2% KA. These results demonstrate tumor-promoting and possible hepatocarcinogenic activity of KA at 2%, but the carcinogenic potential is likely to be weak. This study also indicated that enhanced replication of hepatocytes related to toxic changes might be involved as an underlying mechanism.