Akihiro Hagiwara

Pronounced inhibition by a natural anthocyanin, purple corn color, of 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP)-associated colorectal carcinogenesis in male F344 rats pretreated with 1,2-dimethylhydrazine

The potential of purple corn color (PCC), a natural anthocyanin, to modify colorectal carcinogenesis was investigated in male F344/DuCrj rats, initially treated with 1,2-dimethylhydrazine (DMH), receiving 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the diet. After DMH initiation, PCC was given at a dietary level of 5.0% in combination with 0.02% PhIP until week 36. No PCC-treatment-related changes in clinical signs, body weight and food consumption were found. Incidences and multiplicities of colorectal adenomas and carcinomas in rats initiated with DMH were clearly increased by PhIP. In contrast, lesion development was suppressed by PCC administration. Furthermore, in the non-DMH initiation groups, induction of aberrant crypt foci by PhIP tended to be decreased by the PCC supplementation. The results thus demonstrate that while PhIP clearly exerts promoting effects on DMH-induced colorectal carcinogenesis, these can be reduced by 5.0% PCC in the diet, under the present experimental conditions.

Carcinogenicity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in the rat.

A total of 10 highly-mutagenic heterocyclic amines have been identified to be carcinogenic in rodents. Among these, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), generally the most abundant with normal cooking procedures, induces mammary and colon carcinomas in rats in a clear dose-dependent manner. In a two-generation exposure (transplacental and trans-breast milk) experiment using Sprague-Dawley rats, an increased risk of mammary adenocarcinoma development was found in the second generation. Excretion of PhIP into the milk and transfer of PhIP to fetuses and neonates with resultant hepatic PhIP-DNA adduct formation were also confirmed. On the other hand, PhIP mammary carcinogenesis was significantly inhibited by coadministration of chlorophyllin or a synthetic antioxidant, 1-O-hexyl-2,3,5-trimethylhydroquinone, in long-term experiments using female F344 rats. The available findings strongly suggest that this food-derived carcinogen might be of importance as an environmental factor in the production of human cancers and that its carcinogenicity could be largely avoided by reducing intake of such compounds or by adoption of appropriate chemopreventive measures.

Promoting effects of various chemicals in rat urinary bladder carcinigenesis initiated by N-nitroso-n-butyl-(4-hydroxybutyl)amine

We studied the capacity of various chemicals to promote urinary bladder cancer in male F344 rats after initiation by N-nitroso-n-butyl-(4-hydroxybutyl)amine (BBN). The rats were given initially 0.01% BBN in the drinking-water for 4 wk and then the test compound in the diet for 34 wk. Effects were judged by measuring the formation of preneoplastic lesions papillary or nodular hyperplasia (PN hyperplasia) of the urinary bladder. Administration of 5%, but not 0.5% (w/w) sodium saccharin in the diet significantly increased the incidence and extent of PN hyperplasia. This finding could be related to the induction of cancers in the rat urinary bladder by high levels of saccharin. Sodium ascorbate (5%). DL-tryptophan (5%) and allopurinol (0.02%) also significantly increased the extent of PN hyperplasia in the affected animals, but other test chemicals, such as acetazolamide (0.35%) and quercetin (5%) did not. The results with sodium saccharin and DL-tryptophan were consistent with previous findings and suggest that sodium ascorbate and allopurinol have promoting activities in urinary bladder carcinogenesis in rats. No correlation was found between the extent of crystalluria and promotion of preneoplastic lesions.

Chronic toxicity of butylated hydroxytoluene in Wistar rats

Abstract Groups of 57 Wistar rats of each sex were maintained on diet containing 0.25 or 1% butylated hydroxytoluene (BHT) for 104 wk; control groups comprised 36 rats of each sex. Treated rats of both sexes showed reduced body-weight gain, relative spleen weight and white-blood-cell count while in the males there was also a reduction in serum triglyceride. BHT-treated animals of both sexes showed increased relative liver weight and total blood cholesterol but increases in red-blood-cell count could be seen only in females and only the males showed increased γ-glutamyltransferase. No significant histological changes were observed in the liver or haematopoietic system to explain these haematological and biochemical changes. Tumours were found in the liver, pancreas, mammary glands, uterus, pituitary gland, adrenal glands and in some other organs of some of the treated rats, but their incidence was not significantly different from that in controls. This experiment showed no carcinogenic effect of BHT on rats.

Lack of Carcinogenicity of Quercetin in F344/DuCrj Rats

Quercetin was administered at dietary levels of 0(control), 1.25 and 5.0% to groups of 50 male and 50 female rats for 104 weeks, and then all animals were maintained without quercetin supplement for a further 8 weeks. At 5.0% quercetin, both sexes showed growth retardation throughout the study. There were no treatment‐ascribed effects regarding clinical signs, mortality, urinalyses or hematology. Although serum glucose in 5.0% quercetin‐treated males was significantly decreased and some relative organ weights in 5.0% groups showed statistically significant increases, these latter changes seemed to be related to the growth retardation. An increased incidence of non‐neoplastic hyperplastic polyps in the cecum was noted in the 5.0% males. The incidences of cystic changes and fibroadenomas of the mammary gland, and foci (areas) of hepatocellular alteration in the 5.0% females, and liver bile duct proliferations in the 5.0% males were significantly decreased. No proliferative lesions of the urinary bladder related to treatment with quercetin were found in any rats. The incidences of several other nonneoplastic and neoplastic lesions which demonstrated statistically significant changes appeared to be related to the growth retardation or to be within the normal range, and therefore none was considered to be significant biologically. Thus, the investigation did not demonstrate any clear carcinogenic effect of quercetin on F344 rats at dietary levels of up to 5.0%.

Post-initiation inhibitory effects of green tea catechins on 7,12-dimethylbenz[a]anthracene-induced mammary gland carcinogenesis in female Sprague–Dawley rats

The dose-dependence of green tea catechin (GTC) effects on 7,12-dimethylbenz[a]anthracene (DMBA)-induced mammary gland carcinogenesis were investigated in female Sprague-Dawley rats. Groups of 20 6-week-old rats were treated with dietary 1, 0.1 or 0.01% GTC for 2 weeks and then basal diet alone for 35 weeks. At the end of week 1, they received a 25 mg/kg body weight intragastric dose of DMBA. Further groups of 20 7-week-old rats each were given an intragastric dose of 25 mg/kg body weight DMBA, and starting 1 week after DMBA treatment they were placed on diet containing 1, 0.1 or 0.01% GTC or basal diet alone for 35 weeks. Control rats were given 1% GTC or basal diet alone. The final incidences and multiplicities of mammary tumors were not significantly different between the groups treated with GTC at the same time as DMBA, compared to the DMBA alone control group. On the other hand, the final multiplicities of mammary tumors in groups treated with 1% GTC (P < 0.05) or 0.01% GTC (P < 0.01), but not 0.1% GTC, after DMBA treatment were significantly decreased as compared to the control value. These results indicate that whereas GTC may inhibit mammary carcinogenesis in the post-initiation stage, the effect is weak and not dose-dependent.

Spontaneous Tumors in Aging (C57BL/6N X C3H/HeN)F1 (B6C3F1) Mice

Spontaneous tumors in untreated (C57BL/6N x C3H/HeN)F1 (B6C3F1) mice used as controls in carcinogenicity tests were recorded. In both sexes, the development of spontaneous tumors was age-related. In 244 male mice, the most common tumors were hyperplastic nodules of the liver, hepatocellular carcinomas, malignant lymphomas/leukemias, lung adenomas, and adenocarcinomas. In 246 female mice, the most common tumors were malignant lymphomas/leukemias, pituitary adenomas, neoplastic nodules of the liver, hepatocellular carcinomas, and lung adenomas. Hepatocellular carcinomas metastasized in 20.3% of the animals with these tumors. Few other tumors except malignant lymphomas and leukemias metastasized. Various tumors of other organs and/or tissues were found at low incidences.

Modifying Effects of Various Chemicals on Preneoplastic and Neoplastic Lesion Development in a Wide‐spectrum Organ Carcinogenesis Model Using F344 Rats

Modifying potentials of various chemicals on tumor development were investigated in a wide‐spectrum organ carcinogenesis model using male F344/DuCrj rats. The animals were treated with N‐nitroso‐diethylamine (100 mg/kg body weight, ip, single injection at the commencement of the study), N‐methyl‐N‐nitrosourea (20 mg/kg body weight, ip, 4 times during weeks 1 and 2) and N‐bis(2‐hydroxypropyl)nitrosamine (0.1% in drinking water, during weeks 3 and 4) for multi‐organ initiation and then were given one of 14 test chemicals including 6 hepatocarcinogens, 7 non‐hepatocarcinogens and 1 non‐carcinogen, or basal diet for 16 weeks. All rats were killed at the end of week 20, and the major organs were carefully examined for preneoplastic and neoplastic lesions. Immunohistochemical demonstration of glutathione S‐transferase‐positivc foci was also used for quantitative assessment of liver preneoplastic lesion development. Modifying effects were shown for 11 out of 14 test agents in the liver, forestomach, glandular stomach, lung, urinary bladder or thyroid, 7 of them targeting more than two organs. This was the first demonstration to our knowledge that cloflbrate possesses enhancing potential for urinary bladder carcinogenesis and an inhibiting effect on thyroid carcinogenesis. Caprolactam showed no effect in any organ, in agreement with its established inactivity. The results indicated that the system could be reliably applied as a medium‐term multiple organ bioassay for assessment of the modification potential of test agents in unknown target sites.

The chronic hepatic or renal toxicity of di(2-ethylhexyl) phthalate, acetaminophen, sodium barbital, and phenobarbital in male B6C3F1 mice: autoradiographic, immunohistochemical, and biochemical evidence for levels of DNA synthesis not associated with carcinogenesis or tumor promotion

Male B6C3F1 mice, 6 weeks of age, were fed diets or water containing di(2-ethylhexyl) phthalate (DEHP) at 12,000 or 6000 ppm, acetaminophen (ACT) at 10,000 or 5000 ppm, sodium barbital (BBS) at 1000 ppm, or phenobarbital (PB) at 500 ppm for 40 weeks. Groups of six mice were terminated at 2, 8, 24, and 40 weeks for evaluation of liver and kidney weights, histopathology, and thymidine kinase (TK) activity in liver and kidney and levels of DNA synthesis, measured by tritiated thymidine [( 3H]T) autoradiography or bromodeoxyuridine (BrdU) immunohistochemistry. Liver weights, as percentage of body weight, were significantly elevated at most time intervals for mice exposed to all chemicals at each dose. The hepatocyte labeling indices (LI) with [3H]T autoradiography or BrdU immunocytochemistry were significantly elevated in mice fed DEHP at 12,000 ppm at 24 and 40 weeks or BBS and ACT at 2 weeks. LI were not elevated in mice fed PB. Hepatic TK activity was significantly elevated in mice fed DEHP, BBS, or ACT at Weeks 2 and 8. Histopathologic hepatic lesions were associated with these elevations, while hepatic lesions were not associated with changes in TK activity in PB-treated mice. In contrast, only DEHP and BBS induced toxic renal lesions. Persistent or transient elevation of the renal LI and TK activity accompanied renal toxicity. Thus, the hepatic toxin DEHP induced chronic renal hyperplasia without evidence of renal carcinogenicity or tumor promotion in previous studies at the doses used. ACT, a hepatotoxin, produced transient chronic hepatic hyperplasia without evidence of carcinogenicity in B6C3F1 mice in earlier studies at the same doses used. Thus, persistent or transient hepatic or renal hyperplasia was associated with carcinogenic or tumor promoting activity of these chemicals in some cases but not in others.

Lack of carcinogenicity of butylated hydroxytoluene on long-term administration to b6c3f1 mice

Groups of approximately 50 male and 50 female B6C3F1 mice were given butylated hydroxytoluene (BHT) at concentrations of 200, 1000 or 5000 ppm in their diet for 96 wk followed by a basal diet for 8 wk and were then killed. Similar groups of male and female controls were given basal diet throughout the 104 wk. Females given 1000 or 5000 ppm BHT and males given 5000 ppm showed reduced weight gain. Neither survival rates nor food consumption differed between experimental and control groups. No significant changes attributable to BHT treatment were found in the haematological examinations or serum and urine analyses. Tumours were found in many organs, especially the lungs, liver, lymph nodes and spleen, in both the experimental and control groups, but none were related to BHT treatment. Thus this experiment provided no evidence of BHT carcinogenicity in mice.