Aflatoxin-albumin adducts: a basis for comparative carcinogenesis between animals and humans.

The study objectives were (a) to correlate AFB1 serum albumin adduct levels with AFB1-DNA adduct levels in liver in different rodent species to determine whether the former could serve as a marker of hepatic DNA adduct levels irrespective of species, and (b) to relate the levels of both adducts to differences in susceptibility to tumor induction by AFB1 in the different species. Finally, an attempt was made to compare the dose response for AFB1-albumin adduct formation in the rodent species with that in human populations exposed environmentally to AFB1. Three strains of rat (Fischer 344, Wistar, and Sprague-Dawley), and one strain each of guinea pig (Hartley), hamster (Syrian golden), and mouse (C57BL) were treated by gavage with up to 14 daily doses of between 1 and 80 mug AFB1/kg body weight. Animals were killed 24 h after 1, 3, 7, or 14 days treatment. A dose response in both AFB1-albumin and AFB1-DNA adducts was seen for all species and strains with steady-state adduct levels at 14 days. In rat strains at 14 days after treatment with 20 mu g/kg, the mean AFB1-albumin levels were between 24 and 26 pg AFB1-lysine equivalent/mg albumin, and the mean AFB1-DNA adduct levels were between 1.5 and 2.5 pmol (8, 9-dihydro-8- (2, 6-diamino-4-oxo-3, 4-dihydro-pyrimid-5-ylforamido-)- 9-hydroxy) AFB1/mg DNA. The level of both adducts was in the following order: rat > guinea pig > hamster > mouse. In the case of AFB1-albumin, the mean adduct level at 14 days in the three rat strains was approximately 1.5, 3.0, and 8-fold higher than in the guinea pig, hamster, and mouse, respectively. When the levels of the albumin and DNA adducts at 14 days were plotted against each other for all species and strains, a correlation was observed (r = 0.83; P = < 0.0001; n = 57; two-tailed test) suggesting a constant relationship between the level of binding of AFB1 to serum albumin and liver DNA. The levels of AFB1-albumin adduct also reflect at least qualitatively the relative susceptibility of the different species to AFB1 carcinogenesis; the rat is sensitive and the hamster and mouse are resistant. The level of AFB1-albumin adduct formed as a function of a single dose of AFB1 in rodents was compared to data from humans exposed environmentally to AFB1. This comparison yielded a value for the three rat strains of between 0.3 and 0.51 pg AFB1-lysine equivalent/mg albumin/1 mu g AFB1/kg body weight and a value for the mouse of <0.025. The best estimate for people from The Gambia and southern China was 1.56 pg/mg albumin for the same exposure. These data suggest that humans exposed to AFB1 form amounts of albumin addducts, and by extrapolation amounts of DNA adducts, closer to those observed in AFB1-sensitive species and 1-2 orders of magnitude higher levels than the AFB1-resistant species.

Duck hepatitis B virus infection, aflatoxin B1 and liver cancer in domestic Chinese ducks.

The oncogenicity of Duck hepatitis B virus (DHBV) is unclear since hepatocellular carcinomas (HCCs) have been reported only in domestic ducks in Qidong, an area of China where hepatitis B virus (HBV) and aflatoxin B1 (AFB1) are risk factors for liver cancer in man. In order to better define the association between DHBV infection, AFB1 and HCC we analysed a series of 16 duck liver samples collected from local farms in Qidong. HCC was found in eight and cirrhosis in one of these samples. Furthermore bile duct proliferation, characteristic of AFB1 exposure in ducks and other animal species, was found in these ducks. Integration of DHBV DNA into cellular DNA was observed in only one out of four DHBV positive HCCs, indicating that viral integration is not prerequisite for tumour development. In four remaining HCCs the polymerase chain reaction (PCR) failed to show any DHBV DNA suggesting that liver tumours do occur in polymerase chain reaction (PCR) failed to show any DHBV DNA suggesting that liver tumours do occur in these ducks in the absence of DHBV infection. In addition, AFB1-DNA adducts were detected by hplc-immunoassay in one such DHBV-negative tumour. In summary we demonstrate that risk factors other than DHBV, including AFB1 exposure, may be important in duck liver carcinogenesis in Qidong.

p53 mutations and aflatoxin B1 exposure in hepatocellular carcinoma patients from Thailand.

The prevalence and type of mutations in the p53 tumour-suppressor gene have been determined in 15 hepatocellular carcinomas (HCC) originating from Thailand. Direct sequencing of exons 5-8 revealed 2 mutations, an AGG to AGT (Arg-->Ser) transversion at codon 249, and an ATC-->AAC (Ile-->Asn) transversion at codon 254. Samples from the Thai patients were analyzed for the presence of aflatoxin-liver DNA and aflatoxin-serum albumin adducts, and all but one were found negative. All the patients were genotyped for glutathione-S-transferase (GST) mu, an enzyme possibly involved in the detoxification of AFB1, and 12 out of 15 had the null genotype. In general, the level of aflatoxin-albumin adducts in sera and the prevalence of p53 mutation at codon 249 in HCC were lower than in other areas at high risk of HCC, including southern China and parts of Africa.

Carcinogenicity of an oxidation product of p-phenylenediamine.

para-Phenylenediamine (p-PD), a widely used aromatic amine in the preparation of commercial oxidative-type hair dyes, has been previously demonstrated to have neither mutagenic activity to Salmonella typhimurium nor carcinogenic activity in rats and mice. In this study, the mutagenicity of p-PD after an oxidation by hydrogen peroxide towards S. typhimurium TA98 and its carcinogenicity in Wistar rats were examined both by topical application to the shaved skin and by s.c. injection. The oxidation product was found to be strongly mutagenic to the bacterial tester strain in the presence of rat liver S-9 fraction. Interestingly, in female rats, both topical application and s.c. injection for 18 months of oxidized p-PD could induce a statistically significant incidence of mammary gland tumors (greater than 50%, P less than 0.05). In addition, uterine tumors and soft tissue tumors of both malignant and benign types were also significantly induced (43% and 57%, P less than 0.05) in the s.c. injection group. On the other hand, tumors of mammary gland and soft tissue were not observed in male rats under similar experimental conditions. However, tumors of other organs including liver, kidney, adrenal gland, thyroid gland, urinary bladder and lung were occasionally observed in male rats of both groups and might be related to the p-PD treatment.