Enhancement of Hepatocellular Proliferative Activity of Kojic Acid in Mice by a Simultaneous Administration of Ascorbic Acid

Abstract

ABSTRACT. To examine the tumor modification activity of kojic acid (KA) by sodium ascorbic acid (AA), 5-week-old male ICR mice were administered intraperitoneally with N-diethylnitrosamine (DEN) as an initiation treatment. Two weeks after the initiation treatment, animals were fed basal diet containing 0 (Group 1: DEN alone) or 3% KA (Group 3: DEN+KA), drinking water containing 5,000 ppm AA (Group 2: DEN+AA) or 3% KA and 5,000 ppm AA (Group 4: DEN+KA+AA) for 6 weeks. One week after the administration of KA and/or AA, all mice were subjected to two-thirds partial hepatectomy. At the end of the experimental period, all surviving mice were sacrificed and removed the liver. The liver weights of the Groups 3 and 4 were significantly increased, and the number of proliferating cell nuclear antigen positive hepatocytes and the gene expressions of Ccnc, Ccnd1, Ercc and Cyp7a1 were significantly increased in the Group 4, as compared to the Group 1. These results of the present study suggest that AA enhances the hepatocellular proliferative activity of KA in mice. KEY WORDS: ascorbic acid, hepatocarcinogenesis, kojic acid, mouse.J. Vet. Med. Sci. 69(9): 899-908, 2007 Kojic acid (KA; 5-hydroxy-2(hydroxymethyl)-4-pyrone) is a secondary metabolic product of various species of Aspergillus and Penicillium [23]. It is known that this acid inhibits polyphenol oxidase (tyrosinase) in mushrooms, potatoes, apples and crustaceans [41]. Since polyphenol oxidase catalyzes the conversion of tyrosine to melanin via 3,4-dihydroxyphenylalanine and dopaquinone [21], KA has been used as an inhibitor of polyphenol oxidase in food additives for preventing enzymatic browning of raw crabs and shrimps. In addition, because of its excellent skin whitening properties [35] and inhibitory actions on human melanocyte tyrosinase [28], KA has been applied as a cosmetic agent for the purpose of skin lightening.It has been reported that hepatocellular tumors were induced in B6C3F1 mice that were fed diet containing 3% KA for 20 months [14]. In another study, diet containing 0, 1.5 or 3% KA was administered to heterozygous p53-deficient mice of the CBA strain [p53 (+/-) mice] and their wild-type littermates [p53 (+/+) mice] for 26 weeks [50]. In the study, the incidences of hepatocellular adenomas as well as altered hepatocellular foci were increased in p53 (+/-) and p53 (+/+) mice of KA-treated groups with and/or without initiation, as compared to those in the untreated control mice. In our previous confirmation study using CBA wildtype mice, the incidence of proliferative lesions was significantly increased in the liver of mice that were fed diet containing 1% KA for 26 weeks [51]. In addition, it has recently been reported that a 20-week dietary administration of 2% KA increases the number and area of glutathione Stransferase placental (GST-P) form positive foci in the liver of F344 rats [49]. These findings suggest the hepatocarcinogenic potential of KA in the liver of rodent species.With regard to the genotoxicity of KA, several in vitro genotoxici...

Concurrent administration of ascorbic acid enhances liver tumor-promoting activity of kojic acid in rats

“…While KA alone did not apparently increase the PCNA-positive proliferating cells, concurrent administration of AA increased liver cell proliferation in this carcinogenesis model. While the endpoint marker for early preneoplastic proliferation is different from that in rats, a similar enhancement by AA has already been shown in a mouse hepatocarcinogenesis model (Kono et al, 2007).…”

“…Light-induced skin tumors in hairless mice were also increased by AA (D'Agostini et al, 2005a). Furthermore, we recently found that AA can enhance the proliferation activity of KA in mice hepatocytes (Kono et al, 2007).…”