A single dose-response effect of aflatoxin B1 on rapid liver cancer induction in two strains of rats

To investigate rapid liver cancer induction in rats by aflatoxin B1 (AFB1), different single oral doses of AFB1 were given to 3 groups of 1-year-old Buffalo and Wistar rats. The animals were treated once and all survivors were killed 6 weeks later. Control animals received an equal volume of solvent (DMSO), and both groups of animals were maintained under identical conditions throughout the period of experiment. The survival rates were 40% with low and medium doses in AFB1-treated Buffalo and Wistar rats, and 0% in the high-dose Buffalo rats. Slight ante-mortem elevations in serum concentrations of glutamic pyruvic transaminase (SGOT) and glutamic oxaloacetic transaminase (SGPT) were indicative of the persistent damage effect of AFB1 at week 6. Total protein and albumin concentrations were not altered. The percent incidence of altered cell foci (areas) and neoplastic nodules was higher in Wistar than in Buffalo rats given a similar low dose. Various stages of well differentiated hepatocellular carcinomas (0.1-0.2 cm in diameter) developed in 3 of 8 Wistar rats. It thus appears that Wistar rats are more susceptible to hepatocarcinogenesis following a single oral dose of AFB1 than Buffalo rats.     

Carcinogenicity of dietary aflatoxin M1 in male Fischer rats compared to aflatoxin B1

Aflatoxin M1 (AFM), an hydroxy metabolite of the potent carcinogenic mycotoxin aflatoxin B1 (AFB) is frequently found in milk and other dairy products. Sufficient amounts of AFM were produced to study the carcinogenicity of this compound. AFM was fed to male Fischer rats starting at 7 weeks up to 21 months of age. Agar-based semisynthetic diets contained 0.0, 0.5, 5.0, and 50.0 micrograms/kg of AFM or 50 micrograms/kg of AFB. Hepatocellular carcinomas were detected in two of 37 rats and neoplastic nodules were found in six of 37 rats fed 50 micrograms/kg AFM between 19 and 21 months. No nodules or carcinomas were observed in the lower AFM dose groups. Nineteen of 20 rats fed a diet containing 50 micrograms/kg of AFB developed hepatocellular carcinomas by 19 months of age. Carcinogenic potency of the aflatoxins was reflected by morphometric quantitation of foci detected in hematoxylin and eosin stained sections. Three rats fed the diet containing 50 micrograms/kg AFM developed intestinal carcinomas. None were observed in other groups. Under the conditions of this experiment AFM was found to be a weak hepatic carcinogen compared to AFB and to possess intestinal carcinogenicity.     

Effects of phenobarbital and secondary bile acids on liver, gallbladder, and pancreas carcinogenesis initiated by N-nitrosobis (2-hydroxypropyl)amine in hamsters

The effects of dietary administration of phenobarbital [(PB) CAS: 50-06-6] or the secondary bile acids, deoxycholic acid [(DCA) CAS: 83-44-3] and lithocholic acid [(LCA) CAS: 434-13-9], on tumorigenesis in the liver, gallbladder, and pancreas were investigated in male Syrian golden hamsters after carcinogenic initiation by N-nitrosobis(2-hydroxypropyl)amine [(BHP) CAS: 53609-64-6]. BHP [500 mg/kg (body wt)] was injected sc once weekly for 5 weeks. The animals were then maintained on a basal diet or a diet containing either 0.05% PB, 0.1% DCA, 0.5% DCA, or 0.5% LCA for 30 weeks. DCA enhanced the development of cholangiocarcinomas without influencing that of hepatocellular lesions. PB promoted the induction of hepatocellular carcinomas but not that of cholangiocarcinomas. LCA was without effect on the induction of either hepatocellular carcinomas or cholangiocarcinomas. DCA at a dose of 0.5% enhanced the induction of polyps in the gallbladder. Both DCA, at a dose of 0.1%, and LCA significantly enhanced the induction of pancreas carcinomas. PB had no effect on the induction of polyps in the gallbladder or of pancreas carcinomas. These data document that different tumors may be differentially promoted following initiation with a common carcinogen.     

Oncogenicity of hexachlorobenzene

Subchronic and chronic toxicities of hexachlorobenzene (HCB) were studied in both sexes of Swiss mice, Syrian golden hamsters and Sprague-Dawley rats, at dietary dosages of 0, 100 and 200 ppm (mice), and 0, 200 and 400 ppm (hamsters and rats) for 90 days. At day 91, 25/50 animals in each of 18 groups were killed for histology studies. The rest were killed at 6-week intervals until the study was ended. Marked hepatosplenomegaly, enlarged thymuses and lymph nodes, or swollen and granular-looking renal cortices with depressions or nodulary areas were commonly observed. Dose- and sex-dependent progressive changes included toxic-degenerative hepatitis, chronic cirrhosis, hepatomas, bile-duct adenomas and a few hepatocarcinomas in older animals. A generalized lymphohaematopoietic response led to thymic, splenic and nodal lymphosarcomas, especially in female mice. Toxic-tubular nephritis with cortical infarcts developed into regenerative foci and renal adenomas in low incidences. Liver lesions were more prominent in females, while renal changes were most common in male rats. HCB was retested in both sexes of rats at oral doses of 0, 75 and 150 ppm for up to 2 years. At the start, each group contained 94 rats, and four randomly selected rats were killed at weeks 0, 1, 2, 3, 4, 8, 16, 32, 48 and 64 for microscopy. Progressive liver lesions started as hyperaemia and degenerations (4 weeks), and developed into toxic hepatitis, cirrhosis and formation of pre- and neoplastic foci (36 weeks), with hepatomas, bile-duct adenomas and hepatocellular carcinomas (64 weeks) in very high incidences in females and renal adenomas in male rats.     

Carcinogenesis of nitrosomethylundecylamine in Fischer rats.

Nitrosomethylundecylamine was synthesized and administered to Fischer rats by gavage in olive oil solution, at a dose of 46 mg/animal/week for 30 weeks. There were high incidences of hepatocellular carcinomas and cholangiocarcinomas in the liver and of squamous cell carcinomas and alveolar cell adenocarcinomas in the lung. In contrast with the activity of the next higher homolog, nitrosomethyldodecylamine, no bladder tumors were induced.     

N-Nitroso-N-methylurea initiation in multiple tissues for organ-specific tumor promotion in rats by phenobarbital

Effects of phenobarbital [(PB) CAS: 50-06-6], a systemic tumor promoter, on carcinogenesis initiated by the broad-spectrum carcinogen N-nitroso-N-methylurea [(NMU) CAS: 684-93-5] were investigated in F344/NCr rats. Single and divided doses of NMU were evaluated for this purpose in 4-week-old rats of both sexes. Rats received iv injections of either 0.2 mmol NMU/kg (body wt) once or 0.05 mmol NMU/kg (body wt) for 4 weeks (1 injection/wk), followed by or concurrently with PB (0.05% in drinking water) that was continued until the termination of the experiment. Half the rats were killed at 52 weeks and survivors at 80 weeks. At 52 weeks, PB given subsequent to NMU or concurrently with divided doses of NMU significantly enhanced the incidence of thyroid follicular tumors only in male rats. This sex difference in thyroid tumorigenesis was somewhat less pronounced in animals killed at 80 weeks. Only 1 liver cell adenoma occurred in males and none in females given NMU alone. PB given concurrently with divided doses of NMU enhanced the yield of hepatocellular foci/cm2 but had no significant effect on hepatic tumor development. Subsequent exposure to PB, however, significantly promoted hepatocarcinogenesis in rats of both sexes given NMU in divided doses; 50% of males and 40% of females given NMU (0.05 mmol/kg, administered four times) followed by PB had hepatocellular adenomas and carcinomas by 80 weeks. PB did not affect the incidence of any other kind of neoplasms seen in NMU-initiated or control rats. These lesions included squamous cell neoplasms of the skin, oropharynx, and forestomach; nonsquamous epithelial tumors of mammary gland, pituitary body, intestinal mucosa, and urinary bladder; tumors of the central and peripheral nervous system; and mesenchymal tumors of the kidney. A sequence of multiple low doses of NMU appeared to be a convenient and useful systemic, multitissue, tumor-initiation regimen for systematic investigation of organ-specific tumor promotion in rats.     

Cycles of repeated augmentation pressure in rapid production of pancreatic and cholangiocellular carcinomas in hamsters initiated with N-nitrosobis(2-oxopropyl)amine

We previously reported a rapid production model for pancreatic carcinoma development in Syrian hamsters incorporating the principle of selection by resistance to cytotoxicity. In the present experiment, the efficacy of repeated augmentation pressure with regard to generation of pancreatic lesions in hamsters initiated with N-nitrosobis(2-oxopropyl)amine (BOP) was investigated. Forty-eight female Syrian golden hamsters were divided into four groups according to the frequency of augmentation pressure. Group 1 received 70 mg/kg body weight of BOP and three injections of 20 mg/kg BOP. Groups 2-4 received 70 mg/kg BOP followed by one, two or three cycles of augmentation pressure consisting of dl-ethionine on sugar and salt diet, l-methionine and 20 mg/kg BOP. Hamsters were killed 10 weeks after the beginning of the experiment and the resultant incidences of pancreatic carcinomas from groups 1-4 were 0, 30, 50 and 46.2% respectively, the numbers of pancreatic carcinomas increasing with the frequency of augmentation pressure. A 46.2% yield of cholangiocarcinomas was also observed in group 4. The model should be useful for investigation of potential modulating factors since large numbers of lesions can be induced within a total experimental period of only 10 weeks.     

Inhibition of hepatocarcinogenesis by adrenocorticotropin in aflatoxin B1-treated rats.

We examined whether hormones would modify the carcinogenic action of aflatoxin B1 (AFB1). Four groups of inbred Fischer rats received AFB1, 125 mug per animal, weekly per os. In three of the groups, certain hormones were administered simultaneously: One group received 1 U growth hormone (GH) sc weekly, another was given 4 U adrenocorticotropin (ACTH) weekly, and a third received 0.5 U insulin weekly sc. AFB1, ACTH, and insulin were given for 20 weeks; GH was given for only 10 weeks. The control group did not receive hormone adjuvant. In each group, 4 animals were killed at 7, 14, 21, 28, and 35 weeks; the remaining rats were killed at 77 weeks. Their livers were carefully examined and samples prepared for light and electron microscopy. Animals receiving AFB1 and ACTH failed to exhibit hepatocellular carcinoma. On the other hand, malignant lymphoma appeared at 56 weeks in 3 of the 6 surviving males on this regime. AFB1, alone or when given with insulin or GH, caused hepatocellular carcinoma in all animals; in these, lymphoma was not observed. Lymphoma comprised two cell types, each with similar neclear characteristics but differing in their nucleocytoplasmic ratios and in the amount and distribution of cytoplasmic organelles. Alterations leading to hepatocellular carcinoma were examined at various stages of development. "Basophilic hyperplasia" reflected an increase in free ribosomes. "Hyperplastic nodules" were composed of hepatocyte aggregates with characteristics similar to those encountered in the earlier stage. Both the "neoplastic nodules" and hepatocellular carcinomas were formed by cells containing large, "smooth fingerprints" and free ribosomal aggregates. These features supported the concept that AFB1 impairs ribosomal binding to endoplasmic reticulum membranes. The failure of ACTH-treated animals to develop hepatocellular carcinoma was ascribed to the effect of adrenal cortical stimulation upon membrane-polysome binding.     

Enhancing effect of ethanol on aflatoxin B1-induced hepatocarcinogenesis in male ACI/N rats

The modifying effect of ethanol (EtOH) on aflatoxin B1 (AFB1)-induced hepatocarcinogenesis was examined in male ACI/N rats by chronic treatment at the post-initiation phase. Rats received an ip injection of AFB1 (1.5 mg/kg) twice a week for 10 weeks (a total of 20 doses). Following a week of acclimation, they were given 10% EtOH as drinking water for 56 weeks. The effect of EtOH on the hepatocarcinogenesis was evaluated in terms of the incidence of altered hepatocellular foci and neoplasms at the end of the experiment. Exposure to AFB1 alone induced a substantial number of altered foci (6.98 iron-excluding foci/cm2) in rats. The number of altered liver cell foci in rats receiving AFB1 followed by EtOH was significantly increased (26.39 iron-excluding foci/cm2). In the rats given EtOH after AFB1, the total area and mean diameter of both iron-excluding foci and altered foci identified in hematoxylin and eosin-stained sections were significantly higher than in the rats exposed to AFB1 alone. The incidence of liver cell tumors of the group given AFB1 and EtOH (3/15, 20%) was higher than that of the group treated with AFB1 alone (0/14, 0%). Treatment with EtOH alone for 56 weeks did not induce either. These results indicate an enhancing effect of EtOH on AFB1-induced hepatocarcinogenesis when it is given in the promotion phase.     

Carcinogenic effects of infantile and long-term 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment in the mouse

An infantile carcinogenesis assay was carried out with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) injections administered intraperitoneally at 0, 1, 30 and 60 micrograms/kg b.w. doses to (C57BL/6J X C3Hf)F1 (B6C3) and to (C57BL/6J X BALB/c)F1 (B6C) mice, starting from the 10th day of life, once weekly repeated 5 times. Animals were then observed until 78 weeks of age. The induction of thymic lymphomas was related to treatment at 60 micrograms/kg dose level in both sexes of both hybrids, and at 30 micrograms/kg dose level in both sexes of B6C mice and in male but not female B6C3 mice. The incidence of hepatocellular adenomas was increased by TCDD treatment at 60 micrograms/kg dose level in B6C3 of both sexes but not in B6C mice. Hepatocellular carcinomas were seen at increased incidence at 30 and 60 micrograms/kg doses in B6C3 males but not in B6C3 females or in B6C mice of both sexes. The incidence of other tumor types was not related to treatment in both hybrids. A long-term carcinogenesis bioassay with TCDD was carried out in B6C3 mice treated by gavage at 0, 2.5 and 5.0 micrograms/kg b.w. doses from 6 weeks of age, once weekly for 52 weeks. The animals were observed until 110 weeks of age. An increased incidence of hepatocellular adenomas and carcinomas was related to treatment, at both doses and in both sexes. The incidence of other tumor types was uniformly low in treated and control groups, without any association with treatment, in both sexes.     

Minimal dose and time protection by lindane (gamma-isomer of 1,2,3,4,5,6 hexachlorocyclohexane) against liver tumors induced by aflatoxin B1

This study was carried out in order to investigate the minimal exposure to lindane (LD, 99.72% gamma isomer of 1,2,3,4,5,6 hexachlorocyclohexane), a chlorinated hydrocarbon insecticide, required to protect against liver tumor induced by aflatoxin B1 (AFB1). Materials fed to Buffalo strain rats were as follows: LD 100 ppm; AFB1 1 ppm, LD 100 ppm plus AFB1 1 ppm; and control basal diet. The experimental animals were clinically observed and then serially killed at 1, 3, 5, 10, 15 and 82 weeks. Concurrent administration of LD with AFB1 to rats for more than 3 weeks totally inhibited the incidence of AFB1-induced hepatocellular carcinomas by week 82. Only 1 of 20 rats (5%) fed the same regimen for 1 week developed liver tumors. Animals given 1 ppm AFB1 singly for 15 weeks had a high liver tumor incidence (31.5%). No animals developed liver tumors in LD-treated and control groups. LD may inhibit AFB1-induced liver tumors by stimulating hepatic metabolism and excretion of AFB1 so that less carcinogen is available to liver tissue.     

Species and sex differences of aflatoxin B1-induced glutathione S-transferase placental form in single hepatocytes.

Species and sex differences of aflatoxin B1 (AFB1)-induced glutathione S-transferase placental form (GST-P) positive single hepatocytes have been investigated 48 h after an intraperitoneal injection of AFB1 to young male and female Fischer rats (2 mg AFB1/kg body wt) and male Syrian golden hamsters (6 mg AFB1/kg body wt). The presence of GST-P positive hepatocytes was examined by the immunohistochemical method. Male rats formed three times as many AFB1-induced GST-P positive hepatocytes as females. Pretreatment of both male and female rats with an inhibitor of GSH synthesis, buthionine sulfoximine (BSO) (4 mmol/kg body wt), 2 h and 4 h before AFB1 injection increased AFB1-induced GST-P positive hepatocytes by about 120% above the controls. Male hamsters formed several-fold less AFB1-induced GST-P positive hepatocytes than male rats. Pretreatment with BSO did not increase AFB1-induced GST-P positive hepatocytes in hamsters even though it produced an increase in hepatic necrosis. It appears that GSH and GSH S-transferases play an important role in modulating hepatic AFB1-DNA binding and AFB1-induced GST-P positive hepatocytes in rats and hamsters.     

Modification of pancreatic carcinogenesis in the hamster model. IX. Effect of pancreatitis

The effect of acute and recurrent pancreatitis was investigated in pancreatic cancer induction by N-nitrosobis(2-oxopropyl)amine (BOP) in Syrian golden hamsters. For the correlation of the cellular alteration with carcinogenesis, BOP (20 mg/kg body wt) was injected once sc into hamsters at day 3 (group 2), week 1 (group 3), and week 8 (group 4), corresponding to cellular degeneration, regeneration, and healing, respectively. Additional groups received BOP 30 minutes before common duct ligation for 48 hours (group 1) or before repeated induction of pancreatitis at 4 weekly intervals for 4 weeks (group 5). Group 6 was a pancreatitis control. Two groups of hamsters received BOP only, at the age of 8 weeks (group 7, which served as a BOP control for groups 1-3 and 5) or at the age of 16 weeks (group 8, the control for group 4). Hamsters were killed 46 weeks after BOP injection (with the exception of group 1 animals, which were killed 52 wk after BOP) to guarantee the same postcarcinogen exposure time in each group. The results showed that BOP, when given during cellular degeneration (group 2) and healing (group 4), induced significantly fewer carcinomas than in the control groups, whereas the tumor pattern was not affected when BOP was given before pancreatitis induction (group 1) or at the time of cellular regeneration (group 3). Recurrent pancreatitis (group 5), however, resulted in carcinomas significantly larger in number and size than those in control group 8. A significantly higher incidence of carcinomas occurred in group 8 controls (treated with BOP at the age of 16 wk) compared to the incidence in group 7 controls (treated with BOP at the age of 8 wk).     

Effect of long-term feeding of nivalenol on aflatoxin B1-initiated hepatocarcinogenesis in mice

Nivalenol, a trichothecene, occurs widely in cereals and foods; our current two-year feeding trial has revealed no tumorigenic activity in female mice. To investigate whether dietary nivalenol modulates the development of aflatoxin B1 (AFB1)-initiated hepatocarcinogenesis, one-week old C57Bl/6 x C3H F1 mice were injected intraperitoneally with 6 mg/kg bw AFB1 and six weeks later fed diets containing 0, 6 or 12 ppm nivalenol for one year. Male mice in all three groups developed hepatocellular carcinomas and adenomas, while the incidences in females were 31% in those given AFB1 alone and 20% and 0 in those given AFB1 with 6 and 12 ppm nivalenol, respectively. These findings indicate that dietary nivalenol suppresses AFB1-initiated hepatocarcinogenesis in female mice, presumably by acting on the promotion step.     

Enhancement of GST-P-positive liver cell foci development by nivalenol, a trichothecene mycotoxin.

In order to elucidate whether T-2 toxin (T-2) and nivalenol (NIV), the naturally occurring trichothecene mycotoxins in food and feed, are carcinogenic or possess an ability to modulate aflatoxin B1 (AFB1)-induced hepatocarcinogenicity, a medium-term liver bioassay was carried out. F344 male rats were given a single i.p. injection of diethylnitrosamine (DEN, 200 mg/kg), and then fed the test trichothecenes in diet (2 and 5 p.p.m. T-2 or 6 p.p.m. NIV) for 6 weeks beginning 2 weeks after the injection. Some control groups received DEN alone. For synergism between AFB1 and the trichothecenes, DEN-initiated rats as above were given a single i.p. injection of AFB1 (0.5 mg/kg) 2 weeks later and were fed a NIV-containing diet (6 p.p.m.) for 6 weeks. The other control group received the vehicle alone. Control rats not initiated with DEN were also treated with AFB1, NIV or T-2 alone as above. All rats were subjected to a two-thirds partial hepatectomy (PH) at week 3 and killed at week 8, and liver sections were analyzed by glutathione S-transferase placental form (GST-P) expression. In rats that did not receive DEN, AFB1 alone enhanced both the numbers and areas of GST-P-positive foci as reported earlier, while NIV or T-2 alone induced no marked changes. In rats initiated with DEN, AFB1 caused a marked expression of GST-P, and thus the hepatocarcinogenicity of AFB1 was reconfirmed. The expression of GST-P foci in rats fed T-2 or NIV was found to be at background level, indicating that the hepatocarcinogenicity was not predicted for the trichothecene mycotoxins such as T-2 and NIV by this medium-term bioassay system. In the group initiated by DEN followed by AFB1, on the other hand, an elevation of both the numbers and areas of GST-P-positive foci was observed by the subsequent feeding of rats with NIV, and this elevation was statistically significant from the sum totals of individual data of AFB1 or NIV alone. From this evidence, it is predicted that NIV causes an enhancing effect on AFB1-induced hepatocarcinogenesis.     

Toxicity and carcinogenicity of the Fusarium moniliforme metabolite, fumonisin B1, in rats.

A semi-purified corn-based diet containing 50 mg/kg of pure (not less than 90%) fumonisin B1 (FB1), isolated from culture material of Fusarium moniliforme strain MRC 826, was fed to a group of 25 rats over a period of 26 months. A control group of 25 rats received the same diet without FB1. Five rats from each group were killed at 6, 12, 20 and 26 months. The liver was the main target organ in the FB1-treated rats and the hepatic pathological changes were identical to those previously reported in rats fed culture material of F.moniliforme MRC 826. All FB1-treated rats that died or were killed from 18 months onwards suffered from a micro- and macronodular cirrhosis and had large expansile nodules of cholangiofibrosis at the hilus of the liver. Ten out of 15 FB1-treated rats (66%) that were killed and/or died between 18 and 26 months developed primary hepatocellular carcinoma. Metastases to the heart, lungs or kidneys were present in four of the rats with hepatocellular carcinoma. No neoplastic changes were observed in any of the control rats. Chronic interstitial nephritis was present in the kidneys of FB1-treated rats killed after 26 months. No lesions were observed in the esophagus, heart or forestomach of FB1-treated rats and this is contrary to previous findings when culture material of the fungus was fed to rats. It is concluded that FB1 is responsible for the hepatocarcinogenic and the hepatotoxic but not all the other toxic effects of culture material of F.moniliforme MRC 826 in rats.     

Chemoprevention of aflatoxin B1-induced genotoxicity and hepatic oxidative damage in rats by kolaviron, a natural bioflavonoid of Garcinia kola seeds.

The chemopreventive effects of kolaviron, a natural antioxidant bioflavonoid from the seeds of Garcinia kola, on aflatoxin B1 (AFB1)-induced genotoxicity and hepatic oxidative damage was investigated in rats. Kolaviron administered orally at a dose of 200 mg/kg once a day for the first 2 weeks and then 100 mg/kg twice a day for the last 4 weeks of AFB1 (2 mg/kg, single dose, intraperitoneal) treatment reduced the AFB1-increased activities of aspartate amino transferase (AST), alanine amino transferase (ALT) and gamma glutamyltransferase (gamma-GT) by 62%, 56% and 72% respectively. Malondialdehyde (MDA) formation and lipid hydroperoxide (LHP) accumulation were observed in the livers of AFB1-treated rats. Kolaviron significantly reduced the AFB1-induced MDA and LHP formation. Vitamins C and E were protective in reducing the increase in the activities of AST, ALT and gamma-GT as well as lipid peroxidation caused by AFB1 (P<0.01). Administration of rats with kolaviron alone resulted in significant elevation in the activities of glutathione S-transferase, uridyl glucuronosyl transferase and NADH:quinone oxidoreductase by 2.45-, 1.62- and 1.38-folds respectively. In addition, kolaviron attenuated the AFB1-mediated decrease in the activities of these enzymes (P<0.01). Pretreatment of rats with kolaviron, vitamins C and E alone did not exert genotoxicity assessed by the formation of micronucleated polychromatic erythrocytes (MNPCEs) (P>0.05). Co-treatment of rats intraperitoneally with kolaviron (500 mg/kg) 30 min before and 30 min after AFB1 (1 mg/kg) administration inhibited the induction of MNPCEs by AFB1 (P<0.001) after 72 h. While vitamin C was effective in reducing AFB1-induced MNPCEs formation, vitamin E did not elicit any antigenotoxic response. These results indicate kolaviron as effective chemopreventive agent against AFB1-induced genotoxicity and hepatic oxidative stress. Thus kolaviron may qualify for clinical trial in combating the menace of aflatoxicosis in endemic areas of aflatoxin contamination of foods.     

3,2'-Dimethyl-4-aminobiphenyl-induced gallbladder carcinogenesis and effects of ethinyl estradiol in hamsters.

The effects of ethinyl estradiol (EE) on 3,2'-dimethyl-4-aminobiphenyl (DMAB)-induced carcinogenesis were examined in Syrian golden hamsters. DMAB was subcutaneously injected in corn oil at a concentration of 100 mg/kg once a week for 20 weeks and EE was administered in the diet at a dose of 0.75 ppm throughout the experiment. Some animals were killed at week 20 and all surviving ones were killed at week 50. Gallbladder tumors (adenomas and carcinomas) were induced in 6 of 15 hamsters (40%) in the DMAB + EE group and 5 of 14 (36%) in the DMAB alone group in males, and in 6 of 13 (46%) in the DMAB + EE group and 1 of 8 (13%) in the DMAB alone group in females at week 50. A clearer enhancing effect of EE on DMAB gallbladder carcinogenesis was observed for tumor multiplicity (No./animal) for both sexes; from 0.36 to 0.67 in males and from 0.14 to 0.62 in females. Thus, DMAB was demonstrated to be carcinogenic in the gallbladder of hamsters and EE enhanced this DMAB-induced gallbladder tumorigenesis.     

3,2'-Dimethyl-4-aminobiphenyl-induced Gallbladder Carcinogenesis and Effects of Ethinyl Estradiol in Hamsters

The effects of ethinyl estradiol (EE) on 3,2'-dimethyl-4-aminohiphenyl (DMAB)-induced carcinogenesis were examined in Syrian golden hamsters. DMAB was subcutaneously injected in corn oil at a concentration of 100 mg/kg once a week for 20 weeks and EE was administered in the diet at a dose of 0.75 ppm throughout the experiment. Some animals were killed at week 20 and ail surviving ones were killed at week 50. Gallbladder tumors (adenomas and carcinomas) were induced in 6 of 15 hamsters (40%) in the DMAB + EE group and 5 of 14 (36%) in the DMAB alone group in males, and in 6 of 13 (46%) in the DMAB + EE group and 1 of 8 (13%) in the DMAB alone group in females at week 50. A clearer enhancing effect of EE on DMAB gallbladder carcinogenesis was observed for tumor multiplicity (No./animal) for both sexes; from 0.36 to 0.67 in males and from 0.14 to 0.62 in females. Thus, DMAB was demonstrated to be carcinogenic in the gallbladder of hamsters and EE enhanced this DMAB-induced gallbladder tumorigenesis.     

Tumor promotion by the peroxisome proliferator nafenopin involving a specific subtype of altered foci in rat liver

The involvement of tumor promotion in the hepatocarcinogenic action of peroxisome proliferators has not been generally accepted. We studied the effect of nafenopin (NAF) as a model compound in a two-stage initiation-promotion protocol. Carcinogenesis was initiated by a single dose of aflatoxin B1 (AFB1) in female (AFB1, 5 mg/kg) and male (AFB1, 2 mg/kg) Wistar rats. After recovery NAF was fed via the diet, providing a daily dose of 100 mg/kg body weight. Phenobarbital (PB) (50 mg/kg body weight) was fed to female rats as a positive control. The following results were obtained. (a) At weeks 40, 55, 59, and 70, significantly more and larger liver tumors were present in AFB1-NAF-treated rats than in rats receiving either compound alone, and the effect of the combined treatment was clearly more than additive, in three independent experiments including both sexes. This suggests tumor promotion by NAF. Male rats responded more strongly than females. Similarly, PB enhanced the yield of liver tumors. Histologically, tumors were hepatocellular adenoma or carcinoma. In group AFB1-PB the majority consisted of eosinophilic and glycogenstoring cells. However, adenoma and carcinoma of groups AFB1-NAF and O-NAF consisted of weakly basophilic cells. (b) Phenotypically altered foci were evaluated in hematoxylin- and eosin-stained liver sections from the female rats. NAF treatment after AFB1 had little effect on number and size of eosinophilic-clear cell foci and decreased the number of trigroid foci. However, it led to a dramatic increase (20-fold after 70 weeks of NAF treatment) in number and size of foci of a special phenotype that was extremely rare after AFB1 alone and virtually absent in group AFB1-PB. Hepatocytes in these foci are characterized by weak diffuse basophilia and some eosinophilia, similar to the phenotype in adenoma and carcinoma, and by absence of gamma-glutamyltranspeptidase (GGT) expression. Based on these findings, we propose the hypothesis that NAF promotes the development of liver tumors via a mechanism involving amplification of a specific subtype of altered hepatic foci.