thiourea and Adenoma

Topics: Adenoma; Animals; Dogs; Fluorenes; Humans; Iodine; Iodine Radioisotopes; Mice; Neoplasm Metastasis; Neoplasm Transplantation; Neoplasms, Experimental; Neoplasms, Radiation-Induced; Radiation Effects; Radiotherapy; Rats; Sheep; Thiouracil; Thiourea; Thyroid Gland; Thyroid Neoplasms; Thyroidectomy; Transplantation, Homologous

Five chemicals that are known to induce in rats thyroid follicular-cell adenomas and carcinomas were assayed for their ability to induce DNA damage and DNA repair synthesis in primary cultures of human thyroid cells. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the same Comet assay, were obtained after a 20-h exposure to the following subtoxic concentrations of the five test compounds: methimazole from 2.5 to 10mM; nitrobenzene, potassium bromate, N,N'-diethylthiourea and ethylenethiourea from 1.25 to 5mM. Under the same experimental conditions, DNA repair synthesis, as evaluated by quantitative autoradiography, was present in potassium bromate-exposed thyroid cells from all the three donors and in those from two of three donors with either nitrobenzene or ethylenethiourea, but did not match the criteria for a positive response in thyroid cells from any of the donors with methimazole and N,N'-diethylthiourea. Consistently with their ability to induce thyroid tumors, all the five test compounds, administered p.o. in rats in a single dose corresponding to 1/2 LD50, induced a statistically significant degree of DNA fragmentation in the thyroid. These findings suggest that the five test compounds might be carcinogenic to thyroid in humans.

Topics: Adenocarcinoma, Follicular; Adenoma; Animals; Bromates; Carcinogens; Cells, Cultured; DNA Damage; DNA Fragmentation; DNA Repair; Ethylenethiourea; Humans; In Vitro Techniques; Kidney; Liver; Male; Methimazole; Nitrobenzenes; Rats; Rats, Sprague-Dawley; Thiourea; Thyroid Gland; Thyroid Neoplasms

In our previous investigation, which focused on two-stage carcinogenicity in the thyroid, rats were administered N-bis(2-hydroxypropyl)nitrosamine (DHPN), followed by thiourea (TU) over an experimental period of 19 weeks. Simultaneous treatment with a high level of vitamin A (VA) enhanced the induction of proliferative lesions that originated from the thyroidal follicular epithelium. To examine whether hormone synthesis in the thyroid could be inhibited by simultaneous treatment with a large amount of VA and TU, all of the rats were initially given a single subcutaneous injection of 2,800 mg DHPN/kg followed by a supply of 0% TU + 0% VA (DHPN only, control group), 0.2% TU in their drinking water (DHPN/TU group), 0.1% VA in their diet (DHPN/VA group), or 0.2% TU + 0.1% VA (DHPN/TU + VA group) during an experimental period of 4 weeks. Results obtained indicate that the iodine uptake and organification, namely iodination of tyrosine residue in thyroglobulin, of the thyroid, were significantly decreased in the DHPN/TU group compared to the DHPN control group. The variation in these values was attributable to the inhibitory effect of TU upon thyroid hormone synthesis. Results obtained from the DHPN/TU + VA and DHPN/TU groups were comparable. Therefore, the possibility that modification of hormone synthesis contributes to the enhancing effect of simultaneous treatment with a large amount of VA on thyroidal tumor induction by TU is considered to be very minimal.

Topics: Adenoma; Animals; Body Weight; Bromodeoxyuridine; Carcinogens; Drug Synergism; Hyperplasia; Iodine; Liver; Nitrosamines; Organ Size; Pituitary Gland; Rats; Rats, Inbred F344; Thiourea; Thyroid Gland; Thyroid Hormones; Thyroid Neoplasms; Vitamin A

In order to examine modifying effects of simultaneous treatment with large amounts of vitamin A (VA) and thiourea (TU) on the thyroid tumorigenesis in rats, male F344 rats were initiated with N-bis(2-hydroxypropyl)nitrosamine (2800 mg/kg body weight, single s.c. injection), and starting 1 week later received diet containing 0.1% VA (VA group), drinking water containing 0.2% TU (TU group), 0.2% TU + 0.1% VA (TU + VA group) or tap water/basal diet (control group) for 19 weeks. Serum T3 and T4 in the TU and TU + VA groups were significantly decreased as compared to the control group, while serum TSH levels were remarkably increased. The ratios of T3 and T4 decrease and TSH increase in the TU + VA group were remarkably more pronounced than in the TU group. Thyroid neoplastic lesions were only induced in the TU and TU + VA groups. The multiplicity of intracapsular follicular cell proliferative foci in the TU + VA group was significantly increased as compared to the TU group value. Cell proliferation of hypertrophic and subcapsular follicular cells, as well as in hyperplasias, and neoplasias with adenomatous growth pattern was significantly higher in the combined treatment case than after TU alone. In the liver, centrilobular hypertrophy of hepatocytes was seen in the TU and TU + VA groups, this being especially marked in the latter group. In the combined group case the affected cells were strongly positive for GST-P antibody binding. The results of the present study suggest that cell proliferation of thyroid follicular cell proliferative lesions in rats is enhanced by strong TSH stimulation with simultaneous treatment of TU and large amounts of VA.

Topics: Adenoma; Animals; Body Weight; Carcinogens; Cell Division; Drug Synergism; Male; Nitrosamines; Rats; Rats, Inbred F344; Reference Values; Thiourea; Thyroid Gland; Thyroid Neoplasms; Thyrotropin; Thyroxine; Triiodothyronine; Vitamin A

Time course changes in serum TSH and quantitative data for thyroid proliferative lesions in male F344 rats administered N-bis(2-hydroxypropyl)nitrosamine (DHPN: 2000 mg/kg body weight, single s.c. injection) followed by 0.1% thiourea (TU), were assessed at weeks 1, 2, 4, 8, 12 and 16 of treatment. The serum T4 level in the TU group was markedly decreased at week 1 and remained significantly lowered throughout the experiment. Serum TSH levels, in contrast, were elevated up to a peak at around week 4 with a return to the normal range at week 12. Thyroid weights in the TU group were increased significantly in a treatment period-dependent manner. Histopathologically, marked hypertrophy of thyroid follicular cells occurred at the early stage of TU treatment. Proliferative lesions, such as hyperplasia and adenomas, occurred from weeks 2 and 4, respectively, and increased with the later treatment period. The cell proliferative activity of follicular cells, assessed by BrdU incorporation, was high until week 2, but then returned to normal. The initially appearing hyperplasias and adenomas were characterized by marked proliferation but this also greatly decreased at later stages when TSH was no longer elevated. The results of our study thus suggest that a high serum TSH level plays an important role in the early phase of thyroid tumorigenesis and 8 weeks treatment with test substances is sufficient for detection of thyroid tumor promoter potential in two-stage thyroid carcinogenesis models.

Topics: Adenoma; Animals; Body Weight; Carcinogens; Cell Division; Drug Administration Schedule; Hyperplasia; Male; Nitrosamines; Organ Size; Pituitary Gland; Rats; Rats, Inbred F344; Thiourea; Thyroid Diseases; Thyroid Gland; Thyrotropin; Time Factors

An iron chelate, ferric ethylenediamine-N,N'-diacetate [Fe(III)-EDDA], was found to produce hydroxyl radicals with hydrogen peroxide, as determined by both a deoxyribose degradation test and electron spin resonance. Hydroxyl radical production was inhibited not only by adding hydroxyl radical scavengers and catalase, but also by adding superoxide dismutase to the reaction mixture, suggesting that superoxide anion may be involved in the hydroxyl radical production. A single injection of Fe(III)-EDDA (10 mg Fe/kg body wt) to Wistar rats induced thiobarbituric acid reactivity in the kidneys and liver. Repeated injections of Fe(III)-EDDA (10 mg Fe/kg body wt, twice weekly for 3 months) induced a 40% incidence of renal tumors, including renal adenocarcinoma and renal adenoma, 1 year later. These results suggest that Fe(III)-EDDA is an effective free radical producer in vitro and in vivo and that it may be useful in preparing animal models related to iron-dependent free radical damage. The results support our hypothesis that endogenous or exogenous iron, complexed with certain kinds of chelators, promotes free radical-dependent tissue damage and ultimately leads to carcinogenesis in the affected tissue.

Topics: Adenocarcinoma; Adenoma; Animals; Catalase; Cell Transformation, Neoplastic; Deoxyribose; Edetic Acid; Ferric Compounds; Formates; Hydrogen Peroxide; Hydroxyl Radical; Kidney; Kidney Neoplasms; Lipid Peroxidation; Male; Mannitol; Nitrilotriacetic Acid; Rats; Rats, Wistar; Reactive Oxygen Species; Superoxide Dismutase; Superoxides; Thiobarbituric Acid Reactive Substances; Thiourea

Topics: Adenoma; Aflatoxins; Aniline Compounds; Animals; Animals, Newborn; Benzene Derivatives; Biological Assay; Carcinogens; Croton Oil; DDT; Dimethyl Sulfoxide; Ethylamines; Injections, Subcutaneous; Lung Neoplasms; Mice; Nitrogen Mustard Compounds; Nitrosamines; Pharmaceutical Vehicles; Sulfonic Acids; Thiourea; Urethane