Takako Ikeda

Lack of Effect of Soy Isoflavone on Thyroid Hyperplasia in Rats Receiving an Iodine‐deficient Diet

We have reported a dramatic synergism between soy intake and iodine deficiency regarding induction of thyroid hyperplasia in rats. Because isoflavones are active constituents of soybeans, in the present study, their possible contribution was examined. Female F344 rats were divided into 8 groups, exposed to diet containing a 0.2% soy isoflavone mixture (SI), 0.2% SI+iodine deficiency (ID), 0.04% SI, 0.04% SI+ID, 20% defatted soybean (DS) alone, 20% DS+ID, ID alone or basal diet alone for 5 weeks. Thyroid weight was not influenced by SI, but was increased by the ID and DS diets with a further significant increment in the DS+ID group (P<0.01). Compared to the control value, serum T4 was significantly (P<0.01) increased by 20% DS alone and decreased in all groups given the ID treatment (P<0.001). Serum thyroid stimulating hormone (TSH) level was increased by ID, and further enhanced by DS (P<0.01) but not SI. Histopathologically, diffuse hypertrophy and/or hyperplasia of thyroid follicles were observed in the ID‐treated groups, the severity being enhanced by DS but not SI. Proliferating cell nuclear antigen labeling indices (%) were elevated in the ID diet groups and again enhanced by DS, but not SI. These results thus suggest that isoflavones may not be involved in the mechanisms underlying the synergistic goitrogenic effect of soybean with iodine deficiency.

Lack of Modification by Environmental Estrogenic Compounds of Thyroid Carcinogenesis in Ovariectomized Rats Pretreated with N‐bis(2‐hydroxypropyl)nitrosamine (DHPN)

The effects of environmental estrogenic compounds, soy isoflavone mixture (SI), genistein (GEN), and nonylphenol (NP), and the possible goitrogen 3‐chloro‐4‐(dichloromethyl)‐5‐hydroxy‐2(5H)‐furanone (MX), on thyroid carcinogenesis were investigated in ovariectomized (OVX) female rats. Five‐week‐old OVX F344 rats were given a single subcutaneous injection of N‐bis(2‐hydroxypropyl) nitrosamine (DHPN; 2400 mg/kg, body weight) or vehicle alone. Starting 1 week later, GEN (250 or 25 ppm in diet), SI (400 ppm in diet), NP (250 or 25 ppm in diet), MX (30 ppm, in drinking water), sulfadimethoxine (SDM), a known thyroid tumor‐promoter (1000 ppm in drinking water), or β‐estradiol 3‐benzoate (EB), a synthetic estrogen (0.5 mg in cholesterol pellet, s.c.) were administered for 12 weeks. SDM and EB were included as positive controls. At sacrifice the major organs including the thyroid, pituitary, liver, kidney, uterus, vagina, brain and pancreas were collected and histopathological observation was performed. Thyroid weights were significantly increased (P < 0.001) only in the SDM treatment group and pituitary weights were elevated with SDM (P < 0.05) and EB (P < 0.001). Kidney and uterus weights were also significantly increased (P < 0.05) by EB. Histopathologically, proliferative lesions of the thyroid were only observed in the SDM treatment group and of the pituitary in the SDM or EB treatment groups. Renal tubule lesions, uterine squamous metaplasia, vaginal keratinization and telangiectasia of pancreatic islets were also observed with EB. There were no organ weight changes or histopathological lesions in the major organs, including the thyroid, in the GEN, SI, MX or NP treatment groups. Our results thus indicated a lack of modifying effects on thyroid carcinogenesis in female OVX rats, in agreement with our previous finding in males.

Failure of phenethyl isothiocyanate to inhibit hamster tumorigenesis induced by N-nitrosobis(2-oxopropyl)amine when given during the post-initiation phase

The chemopreventive influence of phenethyl isothiocyanate (PEITC) during the post-initiation stage was investigated in the N-nitrosobis(2-oxopropyl)amine (BOP)-initiated hamster tumorigenesis model. A total of 120 female 5-week-old hamsters were divided into six groups. Animals in groups 1-3, each consisting of 30 hamsters, were injected twice, subcutaneously, with BOP 7 days apart to effect initiation. Starting 1 week after the second BOP injection, hamsters in groups 1 and 2 were fed diets supplemented with 6 micromol/g and 3 micromol/g of PEITC, respectively, for 51 weeks. Animals in group 3 received a basal diet as an initiation positive control. Animals in groups 4-6, each consisting of ten hamsters, were given 6 micromol/g or 3 micromol/g of PEITC alone, or were non-treated, matched negative controls for groups 1-3. At the termination of experimental week 52, the incidences and multiplicities of neoplastic lesions in the target organs including the pancreas, lung, liver and kidney were found to be comparable among the BOP-treated groups. The values for pancreatic adenocarcinomas as well as dysplastic lesions tended to increase although without statistical significance. Taken together with our previous finding that PEITC dramatically inhibited the initiation phase of BOP-induced pancreatic and lung tumorigenesis in hamsters, it can be concluded that PEITC specifically exerts chemopreventive effects only when given concomitantly with the carcinogen.

Synergistic Effects of High‐dose Soybean Intake with Iodine Deficiency, but Not Sulfadimethoxine or Phenobarbital, on Rat Thyroid Proliferation

The specificity and dose dependence of the synergistic effects of soybean intake with iodine deficiency on the induction of thyroid proliferation were investigated in female F344 rats. In the first experiment, rats were divided into 6 groups, each consisting of 5 annuals, and fed a basal diet containing 20% gluten, an iodine‐deficient basal diet alone or an iodine‐deficient diet containing 0.2%, 1.0%, 5.0% or 25% defatted soybean for 5 weeks. Soybean feeding synergistically induced thyroid hyperplasias with iodine deficiency only at the 25% dose. In the second experiment, rats were also divided into 6 groups, each consisting of 5 animals, and fed a basal diet, a diet containing 20% defatted soybean, 0.025% Sulfadimethoxine (SDM), 20% defatted soybean+0.025% SDM, 0.05% phenobarbital (PB) or 20% defatted soybean+0.05% PB for 5 weeks. The SDM treatments significantly (P<0.05‐0.01) increased the thyroid weights, but this increase rate was less prominent in the SDM+soybean group than in the SDM alone group. The PB treatment was also associated with a tendency for increase in thyroid weight, but again this was smaller in the PB+soybean group than in the PB alone group. Although the SDM or PB treatments reduced the serum triiodothyronine and thyroxine levels and consequently increased the serum thyroid‐stimulating hormone (TSH) levels, the soybean feeding did not affect or rather attenuated these changes. Our results clearly indicate that soybean feeding does not synergistically enhance the effects of SDM or PB on the rat thyroid. Thus it can be concluded that soybean intake specifically interacts with iodine deficiency in induction of thyroid proliferative lesions in rats, only at high doses.

Modifying effects of 4-phenylbutyl isothiocyanate on N-nitrosobis(2-oxopropyl)amine-induced tumorigenesis in hamsters

The modifying effects of dietary 4-phenylbutyl isothiocyanate (PBITC), given during the initiation stage of carcinogenesis, were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). A total of 120 female 5-week-old hamsters were divided into six groups. Animals in groups 1-3, each consisting of 30 hamsters, were given BOP by two subcutaneous injections, 1 week apart, at a dose of 20 mg/kg body weight, plus 0, 10 or 100 micromol/animal of PBITC in corn oil by gavage 2 h prior to each carcinogen treatment. Ten animals in group 4 served as a vehicle control, and animals in groups 5 and 6, each consisting of ten hamsters, were given 10 and 100 micromol of PBITC alone in corn oil. Sacrifice was 52 weeks after the first BOP injection. The PBITC treatments significantly (P<0.05) inhibited the development of pancreatic ductal dysplasias and adenocarcinomas. Also, lung tumors (adenomas and adenocarcinomas) were significantly (P<0.05) reduced in a dose-dependent manner. In contrast, both hepatocellular and cholangiocellular tumors (adenomas and carcinomas) tended to be or were significantly increased by PBITC. These results, taken together with our previous findings, indicate that the natural isothiocyanate, phenethyl isothiocyanate (PEITC), has a more potent chemopreventive action against BOP-induced tumorigenesis than synthetic isothiocyanates with longer alkyl chains, such as 3-phenylpropyl isothiocyanate (PPITC) and PBITC. Thus, their lipophilicity does not necessarily reflect the chemopreventive potential because the strength of lipophilicity is PEITC

Lack of carcinogenicity of gardenia blue colour given chronically in the diet to F344 rats

The carcinogenicity of gardenia blue colour was examined in Fischer 344 (F344) rats. Groups of 50 males and 50 females were given the material at dietary doses of 0 (control), 2.5 or 5% for 104 weeks and then sacrificed. The doses were selected on the basis of results from a 13-week subchronic toxicity study. A slight increase in relative organ weights of the left lung was observed in male rats of the 5% group. However, no significant differences between the control and treated groups were noted with regard to clinical signs, mortality and haematological findings. A variety of tumours developed in all groups, including the controls, but all were histologically similar to those known to occur spontaneously in F344 rats, and no statistically significant increase in the incidence of any type of neoplastic lesion was found for either sex in the treated groups. Thus, it was concluded that, under the present experimental conditions, gardenia blue colour is not carcinogenic in F344 rats.

Induction of Pancreatic Islet Cell Tumors in Rats by Repeated Intravenous Administration of 4-hydroxyaminoquinoline 1-oxide

The inducibility of pancreatic islet cell tumors by administration of 4-hydroxyaminoquinolin e 1-oxide (4HAQO) was investigated in male 6-week-old Sprague—Dawley rats. Rats were given 4HAQO intravenously at a weekly dose of 5 mg/kg 4 times (group 1) or a single dose of 10 mg/kg (group 2). Control rats received the vehicle alone (group 3). Fifty-six weeks after the first 4HAQO administration, all surviving animals were killed and the pancreas was examined histopathologically, immunohistochemically and ultrastructurally. The incidences and multiplicities of islet cell tumors in groups 1, 2, and 3 were 52.3% (p < 0.05 vs group 2, p < 0.01 vs group 3), 19.2% and 0%, and 0.70/animal (p < 0.05 vs group 2, p < 0.01 vs group 3), 0.23 and 0, respectively. Islet cell carcinomas were induced only in group 1, accounting for 6/44 (26%) tumors. Islet cell hyperplasias were found in 61.4% (p < 0.05 vs group 3), 42.3% and 10.0% of groups 1, 2, and 3, with multiplicities of 0.95 ( p < 0.05 vs groups 2 and 3), 0.54 and 0.20, respectively. As compared with normal islets from control subjects, islet cell tumors showed an increase in the number of insulin positive cells associated with cytological features indicative of enhanced insulin synthesis and secretion, and a decrease in the number of glucagon positive cells without ultrastructural signs of modified secretory activity. Thus our results indicate that repeated intravenous administration of 4HAQO to rats is useful for the induction of islet cell tumors at high incidence.

Organ-dependent modifying effects of oltipraz on N-nitrosobis(2-oxopropyl)amine (BOP)-initiation of tumorigenesis in hamsters

5-(2-Pyrazinyl)-4-methyl-1,2-dithiole-thione (oltipraz), a substituted 1,2-dithiole-3-thione, is known to inhibit tumorigenesis induced by variety of carcinogens in several animal model systems. In the present experiment, the modifying effects of dietary oltipraz, given during N-nitrosobis(2-oxopropyl)amine (BOP) initiation of carcinogenesis, were investigated in Syrian hamsters. A total of 120 six-week-old females were divided into six groups. Groups 1-3 (30 animals each) were thrice given subcutaneous injections of BOP (10 mg/kg, body weight) at 1 week intervals and fed diets supplemented with 400 or 200 ppm of oltipraz or basal diet alone, starting 1 week prior and finishing 1 week after the carcinogen exposure. Groups 4-6 (10 animals each) were similarly treated without application of BOP. At the end of the 52nd experimental week, all surviving animals were autopsied and examined histopathologically for proliferative lesions of the major target organs for BOP tumorigenicity, including pancreas, liver, kidney, and lung. The incidences and multiplicity of adenocarcinomas of the pancreas were higher in groups 1 and 2 than in group 3 although without statistical significance. The incidence of pancreatic duct dysplasias was significantly (P<0.05) increased in group 2 (62.0%) but not in group 1 (50.0%) as compared with group 3 (46.6%). While the incidences of alveolar adenomas and carcinomas were significantly (P<0.05) decreased by the high dose, the multiplicities of hepatocellular adenomas, cholagiocellular carcinomas and gall bladder adenomas were elevated in the BOP/oltipraz groups (P<0.05). The results of the present study suggest that oltipraz exerts organ-dependent modifying effects on BOP-induced carcinogenesis in hamsters when given in the initiation stage.

Suppressive effects of josamycin on the development of altered liver cell foci and chronic nephropathy in a carcinogenicity study.

The carcinogenicity of josamycin was examined in Fischer 344 (F344) rats. Groups of 50 males and 50 females were given the compound in their diet at concentrations of 0 (control), 1.25 or 2.5% for 104-weeks; these dose levels were selected on the basis of the results of a subchronic study, in which animals rather rejected 5% josamycin. All surviving rats were killed at wk 106. A variety of tumours developed in all groups, including the control group, but all the neoplastic lesions were histologically similar to those known to occur spontaneously in this strain of rats, and no statistically significant increase in the incidence of any tumour was found in the treated groups of either sex. Interestingly, the josamycin treatment significantly reduced the development of altered liver cell foci and chronic nephropathy in a dose-dependent manner. Thus, it was concluded that, under the present experimental conditions, josamycin is not carcinogenic in F344 rats.

Influence of Different Dietary Magnesium and Calcium Intake Levels on the Behavior of 28Mg and Magnesium in Mice

Magnesium, the second most important intracellular cation is found in all tissues and may affect many function of the body. Magnesium deficiency can affect the behavior of other trace elements and minerals. Magnesium uptake in normal mice were investigated with 28Mg by tissue biodistribution and autoradiography)[1–3]. The present report describes the effect of varying quantities of dietary magnesium and calcium on the behavior of magnesium and 28Mg in mice organs, in particular the myocardium.