UMLS:C0001430 - FACTA Search

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Query: UMLS:C0001430 (adenoma)
21,222 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activin A belongs to the transforming growth factor-beta superfamily that exerts a wide range of biologic activities on cellular proliferation and differentiation. Although it was suggested that gonadal tissue is the primary site of activin production, several extragonadal sources have subsequently been identified, including human thyrocytes. The goal of the present study was to evaluate serum activin A levels in a series of patients with different thyroid disorders during the active state of the diseases and after recovery. Serum activin A levels were evaluated in 60 healthy subjects (controls), 8 with multinodular nontoxic goiter (MNG), 30 hyperthyroid (15 with Graves' disease (GD), 12 with autonomous hyperfunctioning adenoma (ATA), and 3 with thyrotropin (TSH)-secreting pituitary adenoma, 16 hypothyroid (11 with Hashimoto's thyroiditis and 5 after total thyroidectomy), and 9 patients with resistance to thyroid hormone (RTH) by commercial enzyme-linked immunosorbent assay (ELISA) kit. Patients with GD and ATA showed activin A levels higher than those found in controls and similar to those observed in MNG (GD, 0.74 +/- 0.3 ng/mL; ATA, 0.86 +/- 0.4; and MNG; 1.0 +/- 0.2 vs. controls: 0.39 +/- 0.5, p < 0.001), while in patients with Hashimoto's thyroiditis, total thyroidectomy or RTH activin A levels were similar to those of controls. In conclusion, this study demonstrates that thyroid hyperplasia and hyperfunction result in increased levels of activin A, although the normal levels observed in thyroidectomized patients clearly demonstrate that the thyroid gland is not the predominant source of activin A in normal conditions. Because activin A may exert negative action on thyrocyte proliferation, it is conceivable that activin A hypersecretion in thyroid disorders might represent a counteracting mechanism.
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PMID:Serum activin A levels in different thyroid disorders. 1259 25

A 69-year-old man was referred for elevated thyroid hormone levels. He had no symptoms apart from mild hyperhidrosis and heat intolerance with occasional headaches. Past medical history included a right hemithyroidectomy for a multinodular goiter and Hashimoto's disease. At presentation the patient had a firm, slightly enlarged left thyroid lobe. There were no visual abnormalities, and the rest of the physical findings were unremarkable. Laboratory findings included elevated values of free T4, free T3, total T3, thyrotropin-secreting hormone (TSH), antithyroglobulin, and antimicrosomal antibodies. Normal values were found for cortisol, prolactin, testosterone, follicle-stimulating hormone, luteinizing hormone, alpha-subunit, and thyroid-stimulating immunoglobulin. Thyroid 123I scan showed an increased 5-hour uptake of 23% and a 24-hour uptake of 53% with a diffuse uniform enlargement of the left side. TSH level did not increase after a thyrotropin-releasing hormone stimulation test. Serum sex hormone binding globulin was elevated. Magnetic resonance imaging of the pituitary revealed a pituitary macroadenoma with suprasellar extension to the optic chiasm. Histologic examination of the adenoma after transsphenoidal hypophysectomy showed cells that stained positive for TSH. TSH-secreting pituitary adenomas account for 1% of functioning pituitary tumors and are an exceedingly rare cause of hyperthyroidism. To our knowledge, this is the first report of pituitary tumor inducing hyperthyroidism in the setting of Hashimoto's disease. There is a possibility that TSH elevation related to Hashimoto's disease might have contributed to the development of a TSH-secreting pituitary adenoma.
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PMID:Thyrotropin-secreting pituitary tumor and Hashimoto's disease: a novel association. 1451 96

Pregnenolone-16alpha-carbonitrile (PCN) and Aroclor 1254 (PCB) both reduce serum thyroid hormone levels in rats, but only PCN consistently produces an increase in serum thyrotropin (TSH). PCN-mediated increases in TSH result in increased thyroid follicular cell proliferation and hyperplasia, which may represent early events on a morphological continuum leading to neoplasia. The purpose of this study was to assess whether PCN, a compound that increases serum TSH, and PCB, which does not increase TSH, promote thyroid tumors in a two-stage carcinogenesis model. Male SD rats were administered the thyroid tumor initiator diisopropanolnitrosamine (2.5 g/kg, sc), and after seven days were fed control diet, diet containing 1000 ppm PCN, or diet containing 100 ppm PCB for 19 weeks. Body weights were unaffected by PCN treatment, but were reduced 21% after 19 weeks of PCB treatment compared to control. PCN treatment significantly reduced serum T4 through week 3 before returning to control concentrations, whereas T4 levels following PCB treatment fell below detection limits by week 3 and remained drastically reduced through week 19. TSH concentrations in PCN-treated rats increased three-fold at week 2, then declined to near control values at week 19. After one week of PCB treatment, TSH concentrations reached nearly twice that of controls, and were sustained until week 6. The incidence of thyroid follicular cell proliferative lesions, including cystic and follicular hyperplasia, cystic and follicular adenoma, and follicular carcinoma, was significantly increased following PCN treatment, but not following PCB treatment. PCB treatment caused an increase in thyroid carcinomas (4 of 22 rats) not associated with the proliferative-type lesions produced by PCN, despite an increase in TSH serum concentrations. In conclusion, PCN appears to promote thyroid tumors in a manner consistent with known effects of excessive TSH stimulation. However, thyroid carcinomas stemming from PCB treatment indicate that separate mechanisms exist for the production of thyroid cancer in rodents by chemicals classically considered microsomal enzyme inducers.
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PMID:Promotion of thyroid tumors in rats by pregnenolone-16alpha-carbonitrile (PCN) and polychlorinated biphenyl (PCB). 1520 39

The molecular basis of pituitary tumorigenesis remains controversial, but there are two major theories which have been subject to most investigation: hormonal (usually hypothalamic factors) and/or growth factor overstimulation, or a molecular defect within the pituitary itself. It has been shown, for example, that excessive regulatory hormone stimulation can lead to an increased number of cells in the pituitary in various physiological or pathological states such as pregnancy (lactotrophs), untreated primary hypothyroidism (thyrotrophs and lactotrophs),primary hypoadrenalism (corticotrophs) and ectopic GHRH-secreting tumours (somatotrophs). Animal models also provide data that in the presence of excessive hypothalamic hormone stimulation, adenoma formation can occur. However, evidence in favour of the monoclonal nature of pituitary tumours argues for an intrinsic molecular defect as the primary initiating event in tumour formation. We review the various hormonal factors and their receptors effecting the different types of pituitary cells, such as CRH, AVP and cortisol feedback on corticotrophs; GHRH, Galpha PKA, somatostatin and GH and IGF feedback on somatotrophs; GnRH, LH/FSH, activin and oestrogen feedback on gonadotrophs; dopamine, oestrogen and prolactin feedback on lactotrophs; and TRH, TSH and thyroid hormone feedback on thyrotrophs. The monoclonal origin of adenomas makes it unlikely that hypothalamic factors could initiate pituitary transformation, but they could still create an environment where there is a higher chance that a possible causative tumorigenic mutation may occur in one (or several) of the overstimulated pituitary cells, or enhance the proliferation of an already-mutated cell.
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PMID:Role of regulatory factors in pituitary tumour formation. 1528 40

Herein, we present a case of central thyrotoxicosis with well-documented serial therapeutic interventions. Thyroid-stimulating hormone (TSH)-secreting pituitary tumors represent a rare cause of hyperthyroidism. It is being diagnosed more frequently with the third-generation TSH assay. Many conditions can produce normal or elevated TSH levels in combination with elevated thyroid hormone levels. The differential diagnosis includes resistance to thyroid hormone (RTH, Refetoff's syndrome), assay interference from anti-T4/T3 and heterophile antibodies, elevated or altered binding proteins, drugs affecting peripheral metabolism, and noncompliance with thyroid replacement therapy. In contrast to RTH, our patient presented had high alpha-subunit-to-TSH molar ratio, failed TSH response to thyrotropin-releasing hormone stimulation, and a large pituitary mass. Normal or high TSH in the presence of elevated T4 or T3 is a fairly common clinical scenario with many etiologic possibilities. This TSH-producing adenoma represents an unusual initial clinical presentation, as hypogonadism appeared before features of thyrotoxicosis were appreciated. This case represents the most modern therapeutic approach to the management of this rare disease. Our patient has done well on octreotide with control of thyrotoxicosis and an additional 30% shrinkage of his tumor mass.
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PMID:Thyrotoxicosis presenting as hypogonadism: a case of central hyperthyroidism. 1554 48

4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1,5-a]-pyrimidine (DMP 904) is a potent and selective antagonist of corticotropin releasing factor receptor-1 (CRF1 receptor) with an efficacious anxiolytic profile in preclinical animal models. In subchronic toxicity studies in Sprague-Dawley rats, DMP 904 produced thyroid follicular cell hypertrophy and hyperplasia, and a low incidence of follicular cell adenoma. The current investigations were designed to determine the mode of action by which DMP 904 disrupts thyroid homeostasis in male rats. Five-day treatment with DMP 904 (300 mg/kg/day) dramatically lowered serum thyroxine (T4) to levels below detectable limits (< 1 microg/dl) by 72 h, with concurrent decreases in triiodothyronine (T3, about a 70% decrease) and increases in thyroid stimulating hormone (TSH; about a three-fold increase). DMP 904 increased [125I]T4 total body clearance (Cl tb) (38.21 +/- 10.45 ml/h) compared to control (5.61 +/- 0.59 ml/h) and phenobarbital-treated rats (7.92 +/- 1.62 ml/h). This increase in Cl(tb) was associated with a significant increase in biliary clearance (Cl bile) of unconjugated [125I]T4 (nearly 80-times control rates) and increased liver:blood ratios of T4, suggestive of enhanced hepatic uptake of T4. A single dose of DMP 904 (200 mg/kg) increased mRNA levels of hepatic cytochrome P450s (CYP 3A1 and CYP 2B1) and UDP-glucuronosyltransferases (UGT 1A1 and UGT 1A2). DMP 904 also induced mRNAs of the canalicular transporter, multi-drug resistance protein-2 (Mrp2) and sinusoidal transporters, organic anion transporting proteins (Oatp1 and Oatp2) within 24 h. Western blot analysis confirmed DMP 904 related increases in Oatp2 protein expression. Collectively, these data suggest that DMP 904 is an agonist of the constitutive androstane receptor (CAR) and pregnane X receptor (PXR) and that the decreased serum levels of T4 and T3 resulted from increased hepatobiliary clearance. However, DMP 904 is distinguished from other compounds associated with similar effects on thyroid hormone homeostasis because its effects were primarily related to increased biliary excretion of unconjugated T4.
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PMID:Increased hepatobiliary clearance of unconjugated thyroxine determines DMP 904-induced alterations in thyroid hormone homeostasis in rats. 1567 46

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized they accumulate in adipose tissue resulting in chronic lifetime human exposure. Since human exposure to DLCs always occurs as a complex mixture, the Toxic Equivalency Factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD that is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals, based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation, because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally-related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 3,3',4,4',5-Pentachlorobiphenyl (PCB 126) was produced commercially before 1977 for the electric industry as a dielectric insulating fluid for transformers and capacitors. Manufacture and use of the chemical was stopped because of increased PCB residues in the environment, but it continues to be released into the environment through the use and disposal of products containing PCBs, as by-products during the manufacture of certain organic chemicals, and during combustion of some waste materials. Bioaccumulation of PCB 126 results in persistent levels in animal and human tissues and the biological responses to PCB 126 are similar to those of TCDD, a known human carcinogen. PCB 126 was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and PCBs. The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. PCB 126 was included since this is the most potent coplanar PCB that has dioxin-like activities. While one of the aims of the dioxin TEF evaluation was a comparative analysis across studies, in this Technical Report only the results of the PCB 126 study are presented and discussed. Female Harlan Sprague-Dawley rats were administered PCB 126 (99% pure) in corn oil with acetone by gavage for 14, 31, or 53 weeks or 2 years. 2-YEAR STUDY: Groups of 81 female rats were administered 30, 100, 175, 300, 550, or 1,000 ng PCB 126/kg body weight in corn oil:acetone (99:1) by gavage, 5 days per week, for up to 104 weeks; a group of 81 vehicle control female rats received the corn oil/acetone vehicle alone. A group of 28 rats received 10 ng/kg for up to 53 weeks only. Up to 10 rats per group were evaluated at 14, 31, or 53 weeks. A stop-exposure group of 50 female rats was administered 1,000 ng/kg PCB 126 in corn oil:acetone (99:1) by gavage for 30 weeks then the vehicle for the remainder of the study. Mean body weights of 30 and 100 ng/kg rats were similar to those of the vehicle controls during most of the study, mean body weights of 175 and 300 ng/kg rats were less than those of the vehicle controls during year 2 of the study, and mean body weights of 550 ng/kg, 1,000 ng/kg core study, and 1,000 ng/kg stop-exposure rats were less than those of the vehicle controls after week 17. THYROID HORMONE CONCENTRATIONS: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31- and 53- week interim evaluations. In the 550 and 1,000 ng/kg rats, total thyroxine (T4) and free T4 were significantly lower than vehicle controls and serum triiodothyronine (T3) and thyroid stimulating hormone (TSH) levels were significantly higher than vehicle controls at the 14-week interim evaluation. Serum T3 was also significantly higher in the 300 ng/kg rats compared to vehicle controls at 14 weeks. At 31 weeks, T3 was significantly higher at doses of 100 ng/kg or greater compared to vehicle controls. TSH levels were higher in 550 and 1,000 ng/kg rats than in vehicle controls. At 53 weeks, significantly lower serum concentrations of total T4 and free T4 were observed compared to vehicle controls in groups administered 175 ng/kg or greater and 30 ng/kg or greater, respectively. Serum T3 levels were significantly higher at doses of 175 ng/kg or greater compared to vehicle controls. No changes in TSH were observed between vehicle controls and dosed rats at 53 weeks. HEPATIC CELL PROLIFERATION DATA: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine was conducted at the 14-, 31-, and 53-week interim evaluations. The hepatocellular labeling index was significantly higher at doses of 300 ng/kg or greater at 14 weeks and 175 ng/kg or greater at 31 weeks compared to vehicle controls. No statistically significant differences were observed between vehicle controls and PCB 126 dosed rats at 53 weeks. However at 53 weeks, a 5.8-fold increase above the vehicle controls was observed in the 1,000 ng/kg group. CYTOCHROME P450 ENZYME ACTIVITIES: To evaluate the expression of known dioxin-responsive genes, CYP1A1 associated 7-ethoxyresorufin-O-deethylase (EROD) activity and CYP1A2-associated acetanilide 4-hydroxylase (A-4-H) activity were evaluated at the 14-, 31-, and 53-week interim evaluations. In addition, CYP2B associated pentoxyresorufin-O-deethylase (PROD) activity was also analysed. Hepatic PROD (CYP2B1) and hepatic and pulmonary EROD (CYP1A1) activity were significantly greater in all dosed groups than in vehicle controls at weeks 14, 31, and 53. Hepatic A-4-H (CYP1A2) activity was significantly greater in the 30, 100, 175, 300, 550, and 1,000 ng/kg groups compared to vehicle controls at weeks 14, 31, and 53. DETERMINATIONS of PCB 126 CONCENTRATIONS IN TISSUES: The tissue disposition of PCB 126 was analyzed in the liver, lung, fat, and blood of all rats in vehicle controls and all dosed groups at the 14-, 31-, and 53-week interim evaluations and in 10 rats per group including vehicle controls at the end of the 2-year study (104 weeks). Detectable concentrations of PCB 126 were observed in the liver, fat, lung, and blood. Measurable concentrations of PCB 126 were present in the liver and fat at weeks 31, 53, and 104. Hepatic and fat concentrations increased with increasing doses of PCB 126. Measurable concentrations of PCB 126 were present in vehicle control lung tissue at 53 and 104 weeks. No PCB 126 was observed in the blood from the vehicle control rats. Lung and blood concentrations tended to increase with increasing doses of PCB 126, with a few exceptions. In the stop-exposure group, PCB 126 concentrations in liver and fat were lower than the levels observed in the 30 ng/kg group. In the stop-exposure group, lung tissue PCB 126 concentrations were equivalent to the levels observed in the 30 ng/kg group. In blood from the stop-exposure group, PCB 126 concentrations were equivalent to the levels observed in the 100 ng/kg group. PATHOLOGY AND STATISTICAL ANALYSES: Absolute and relative liver weights were significantly increased at all time points and correlated with increased incidences of hepatocellular hypertrophy. At 2 years, there were significant treatment-related increases in the incidences of cholangiocarcinoma and hepatocellular adenoma. Three hepatocholangiomas were seen in the 1,000 ng/kg core study group and a single incidence of cholangioma each occurred in the 550 and 1,000 ng/kg core study groups. At 2 years, a significant dose-related increase in hepatic toxicity was observed and was characterized by increased incidences of numerous lesions including hepatocyte hypertrophy, multinucleated hepatocytes, diffuse fatty change, bile duct hyperplasia, bile duct cyst, oval cell hyperplasia, necrosis, pigmentation, inflammation, nodular hyperplasia, portal fibrosis, cholangiofibrosis, and toxic hepatopathy. The incidences of these lesions were generally decreased in the 1,000 ng/kg stop-exposure group compared to the 1,000 ng/kg core study group. The lung weights of 1,000 ng/kg rats were generally significantly increased at weeks 14, 31, and 53. At 2 years, treatment related increases in the incidences of cystic keratinizing epithelioma and squamous cell carcinomas were observed. In addition, dose-related increases in the incidences of bronchiolar metaplasia of the alveolar epithelium and squamous metaplasia were also observed. The incidence of gingival squamous cell carcinoma of the oral mucosa was significantly increased in the 1,000 ng/kg core study group at 2 years. Gingival squamous cell carcinoma, although reduced in incidence as compared to the 1,000 ng/kg core study group, was still present in the 1,000 ng/kg stop-exposure group. At 2 years, adenomas and/or carcinomas were present in the adrenal cortex of most core study groups and in the 1,000 ng/kg stop-exposure group. Dose-related effects on the incidences of adrenal cortex atrophy and cytoplasmic vacuolization were also seen. (ABSTRACT TRUNCATED)
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PMID:NTP toxicology and carcinogenesis studies of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) (CAS No. 57465-28-8) in female Harlan Sprague-Dawley rats (Gavage Studies). 1662 45

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized, they accumulate in body tissue, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always involves a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, which is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. TCDD is not manufactured commercially other than for scientific research purposes. The main sources of TCDD releases into the environment are from combustion and incineration; metal smelting, refining, and processing; chemical manufacturing and processing; biological and photochemical processes; and existing reservoir sources that reflect past releases. TCDD (dioxin) was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and PCBs. The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. While one of the aims of the dioxin TEF evaluation was a comparative analysis across studies, in this Technical Report, only the TCDD results are presented and discussed. TCDD was included because it is the reference compound for the dioxin TEF methodology. Female Harlan Sprague-Dawley rats were administered TCDD (at least 98% pure) in corn oil:acetone (99:1) by gavage for 14, 31, or 53 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, L5178Y mouse lymphoma cells, cultured Chinese hamster ovary cells, Drosophila melanogaster, and mouse bone marrow cells. 2-YEAR STUDY: Groups of 81 or 82 female rats were administered 3, 10, 22, 46, or 100 ng TCDD/kg body weight in corn oil:acetone (99:1) by gavage, 5 days per week, for up to 105 weeks; a group of 81 vehicle control female rats received the corn oil/acetone vehicle alone. Up to 10 rats per group were evaluated at 14, 31, or 53 weeks. A stop-exposure group of 50 female rats was administered 100 ng/kg TCDD in corn oil:acetone (99:1) by gavage for 30 weeks and then just the vehicle for the remainder of the study. Survival of dosed groups was similar to that of the vehicle control group. Mean body weights of 100 ng/kg core study and stop-exposure groups were less than those of the vehicle control group after week 13 of the study. Mean body weights of 46 ng/kg rats were less than those of the vehicle controls during year 2 of the study, and those of 22 ng/kg rats were less than those of the vehicle controls the last 10 weeks of the study. THYROID HORMONE CONCENTRATIONS: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31- and 53-week interim evaluations. At 14 weeks, there were significant decreases in serum total and free thyroxine (T4) levels and increases in serum total triiodothyronine (T3) and thyroid stimulating hormone (TSH). At 31 weeks, there were significant decreases in serum total and free T4 levels and increases in serum total T3 but no significant effect on TSH. At 53 weeks, there were significant decreases in serum total T4 levels and increases in serum total T3. There were no significant effects on total T4 or TSH levels. HEPATIC CELL PROLIFERATION DATA: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine was conducted at the 14-, 31-, and 53-week interim evaluations. The hepatocellular labeling index was significantly higher in the 22 ng/kg group compared to vehicle controls at 14 weeks. At the 31-week interim evaluation, the labeling indices in hepatocytes were significantly higher in all dosed groups than in the vehicle controls. At 53 weeks, labeling indices were significantly higher in the 46 and 100 ng/kg groups than in the vehicle controls. CYTOCHROME P450 ENZYME ACTIVITIES: To evaluate the expression of known dioxin-responsive genes, CYP1A1-associated 7-ethoxyresorufin-O-deethylase (EROD) activity and CYP1A2-associated acetanilide-4-hydroxylase (A4H) activity were evaluated at 14, 31, and 53 weeks. In addition, pentoxyresorufin-O-deethylase (PROD) activity was analyzed. Hepatic EROD, PROD, and A4H activities were significantly higher in all dosed groups relative to vehicle controls at the 14-, 31-, and 53-week interim evaluations. Pulmonary EROD was also significantly higher in all dosed groups compared to vehicle controls at 14, 31, and 53 weeks. DETERMINATIONS OF TCDD CONCENTRATIONS IN TISSUES: The tissue disposition of TCDD was analyzed in the liver, lung, fat, and blood of all animals in each group at the 14-, 31-, and 53-week interim evaluations and in 10 animals per group at the end of the 2-year study (105 weeks). The highest concentrations of TCDD were observed in the liver, followed by fat tissue. Liver and fat tissue concentrations of TCDD increased with increasing doses of TCDD. No measurable concentrations of TCDD were observed in blood from vehicle control or treated rats at any of the interim evaluations. Mean levels of TCDD in the liver and fat in the 100 ng/kg group at the end of the 2-year study were 9.3 and 3.2 ng/g, respectively. In liver tissue from the stop-exposure group, TCDD concentrations were slightly higher than those observed in the 3 ng/kg group. In the stop-exposure group, TCDD concentrations in fat were below the limits of quantitation. PATHOLOGY AND STATISTICAL ANALYSES: Absolute and/or relative liver weights were increased at 14, 31, and 53 weeks, with more severe effects occurring in the higher dosed groups. Increased liver weights correlated with increased incidences of hepatocyte hypertrophy at 14, 31, and 53 weeks. Exposure led to a treatment-related increase in hepatic toxicity with a broad spectrum of lesions. Incidences and severities of lesions increased at higher doses and longer durations of exposure. The earliest effects were increased incidences and severities of hepatocyte hypertrophy at 14 weeks. At 2 years, there was a significant increase in toxic hepatopathy characterized by increased incidences of numerous nonneoplastic liver lesions including hepatocyte hypertrophy, multinucleated hepatocytes, altered hepatocellular foci, inflammation, pigmentation, diffuse fatty change, necrosis, portal fibrosis, oval cell hyperplasia, bile duct hyperplasia, bile duct cysts, cholangiofibrosis, and nodular hyperplasia At 2 years, the incidence of hepatocellular adenoma was significantly increased in the 100 ng/kg core study group. Dose-related increased incidences of cholangiocarcinoma were seen in core study rats administered 22 ng/kg or greater. The highest incidence of cholangiocarcinoma was seen in the 100 ng/kg core study group and included a significant number of animals with multiple cholangiocarcinomas. Two cholangiocarcinomas and two hepatocellular adenomas were seen in the 100 ng/kg stop-exposure group. Two hepatocholangiomas were seen in the 100 ng/kg core study group, and one cholangioma was seen in the 100 ng/kg stop-exposure group. In the lung, the incidence of cystic keratinizing epithelioma of the lung was significantly increased at 2 years in the 100 ng/kg core study group. Nonneoplastic effects in the lung included increased incidences of bronchiolar metaplasia. The incidence of gingival squamous cell carcinoma of the oral mucosa was significantly increased in the 100 ng/kg core study group at 2 years and was accompanied by an increased incidence of gingival squamous hyperplasia. At 2 years, the incidence of squamous cell carcinoma of the uterus in the 46 ng/kg group was significantly increased, and there were two squamous cell carcinomas in the 100 ng/kg stop-exposure group. At 2 years, one acinar adenoma and two acinar cell carcinomas of the pancreas were seen in the 100 ng/kg core study group; one acinar carcinoma was seen in the 100 ng/kg stop-exposure group. The incidences of acinar cell adenoma or carcinoma (combined) exceeded the historical vehicle control range. Nonneoplastic effects in the lung included acinar cytoplasmic vacuolization, chronic active inflammation, acinar atrophy, and arterial chronic active inflammation. (ABSTRACT TRUNCATED)
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PMID:NTP technical report on the toxicology and carcinogenesis studies of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (CAS No. 1746-01-6) in female Harlan Sprague-Dawley rats (Gavage Studies). 1683 33

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bioconcentrate through the food chain. Due to their lipophilicity and persistence, once internalized they accumulate in human tissues, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always involves a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, which is the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals, based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 2,3,4,7,8-Pentachlorodibenzofuran (PeCDF) is not manufactured commercially other than for scientific research purposes. The main sources of PeCDF releases into the environment are from combustion and incineration sources. PeCDF was selected for study by the National Toxicology Program as a part of the dioxin TEF evaluation to assess the cancer risk posed by complex mixtures of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and PCBs. The dioxin TEF evaluation includes conducting multiple 2-year rat bioassays to evaluate the relative chronic toxicity and carcinogenicity of DLCs, structurally related PCBs, and mixtures of these compounds. While one of the aims of the dioxin TEF evaluation was a comparative analysis across studies, in this Technical Report only the results of the present PeCDF study are presented and discussed. Female Harlan Sprague-Dawley rats were administered PeCDF (at least 97% pure) in corn oil:acetone (99:1) by gavage for 14, 31, or 53 weeks or 2 years. 2-YEAR STUDY: Groups of 81 female rats were administered 6, 20, 44, 92, or 200 ng PeCDF/kg body weight in corn oil:acetone (99:1) by gavage, 5 days per week, for up to 105 weeks; a group of 81 vehicle control female rats received the corn oil/acetone vehicle alone. Up to 10 rats per group were evaluated at 14, 31, and 53 weeks. A stop-exposure group was administered 200 ng/kg PeCDF in corn oil:acetone (99:1) by gavage for 30 weeks and then the vehicle for the remainder of the study. The PeCDF in this study was at least 97% pure. Survival of dosed groups was similar to that of the vehicle control group. Mean body weights of the 200 ng/kg core and stop-exposure groups were less than those of the vehicle controls during year 2 of the study. Thyroid Hormone Concentrations: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31- and 53-week interim evaluations. There were significant decreases in total serum thyroxine (T(4)) levels at the 14-week interim evaluation. There were no significant differences observed in serum free T(4), total triiodothyronine (T(3)), or thyroid stimulating hormone (TSH) at 14 weeks. At both 31 and 53 weeks, there were treatment-related decreases in free and total T(4) concentrations and increases in serum T(3) levels. Serum TSH levels in dosed groups at 31 and 53 weeks were not significantly different than in the vehicle controls. Hepatic Cell Proliferation Data: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine (BrdU) was conducted at the 14-, 31-, and 53-week interim evaluations. At 14 and 53 weeks, hepatocyte BrdU-labeling indices were significantly higher in the 200 ng/kg groups compared to time-matched vehicle controls. No significant differences were observed between the dosed groups and vehicle controls at 31 weeks. Cytochrome P450 Enzyme Activities: To evaluate the expression of known dioxin-responsive genes, CYP1A1-associated 7-ethoxyresorufin-O-deethylase (EROD) activity and CYP1A2-associated acetanilide-4-hydroxylase (A4H) activity were evaluated at the 14-, 31-, and 53-week interim evaluations. Hepatic EROD and A4H activities were significantly higher in all groups administered PeCDF relative to the vehicle controls at all three interim evaluations. Pulmonary EROD was also significantly higher in all dosed groups compared to vehicle controls at 14, 31, and 53 weeks. Determinations of PeCDF Concentrations in Tissues: The tissue disposition of PeCDF was analyzed in the liver, lung, fat, and blood of all animals at the 14-, 31-, and 53-week interim evaluations, and in 10 animals per group at the end of the 2-year study (105 weeks). In the liver of vehicle controls, PeCDF concentrations were detectable at 105 weeks. Measurable concentrations of PeCDF were not detected in fat or lung from vehicle control rats at any of the interim evaluations or at 105 weeks. Hepatic and fat concentrations were higher in groups with increasing doses of PeCDF, demonstrating a dose-related increase in tissue burden of PeCDF at each time point. No measurable concentrations of PeCDF were detected in the lungs of vehicle controls or any of the dosed groups at 14 weeks or in the lungs of the vehicle control group at 31, 53, and 105 weeks, or the 6 ng/kg group at 31 and 53 weeks. In groups with measurable levels, PeCDF concentrations were higher with respect to increasing doses. Mean levels of PeCDF in the liver, fat, lung, and blood in the 200 ng/kg group at the end of the 2-year study were 500 ng/g, 7.75 ng/g, 0.28 ng/g and 0.04 ng/mL, respectively. Negligible PeCDF concentrations were observed in blood of the 200 ng/kg group at 53 weeks and the 92 and 200 ng/kg groups at 105 weeks. In liver and fat from the stop-exposure group, the PeCDF concentrations were between the levels observed in the 6 and 20 ng/kg groups. In the stop-exposure group, PeCDF concentration in lung was comparable to levels observed in the 6 ng/kg group. No measurable concentrations were observed in blood from the stop-exposure group. Pathology and Statistical Analyses: There were dose-dependent increases in both absolute and relative liver weights at 4, 31, and 53 weeks, and these tended to correlate with increased incidences of hepatocellular hypertrophy. In the liver at 14 weeks, the only significant effect was an increase in the incidences of hepatocellular hypertrophy. At 53 weeks, there were significant increases in the incidences of hepatocellular hypertrophy and pigmentation. At 2 years, there were significant dose-dependent trends for increased incidences of hepatocellular adenoma and cholangiocarcinoma of the liver. A significant dose-dependent increase in hepatic toxicity was observed and was characterized by increased incidences of numerous nonneoplastic lesions including hepatocellular hypertrophy, multinucleated hepatocytes, oval cell hyperplasia, diffuse fatty change, pigmentation, nodular hyperplasia, eosinophilic foci, hepatocellular necrosis, bile duct hyperplasia, bile duct fibrosis, cholangiofibrosis, and toxic hepatopathy. At 2 years, three gingival squamous cell carcinomas of the oral mucosa were seen in the 200 ng/kg core and stop-exposure groups, two occurred in the 6 ng/kg group, and one occurred in each of the vehicle control, 20 ng/kg, and 92 ng/kg groups. Gingival squamous hyperplasia occurred in all groups including the vehicle controls, with increasing incidences in groups administered 44 ng/kg or greater. The incidence of carcinoma of the uterus was marginally increased in the 92 ng/kg group at 2 years. Increased incidences of chronic active inflammation of the uterus were observed in all dosed groups, and the incidence in the 200 ng/kg stop-exposure group was greater than those in the vehicle control and 200 ng/kg core study groups. Increased incidences of squamous metaplasia of the uterus occurred in all dosed groups. In the 200 ng/kg stop-exposure group, the incidence of squamous metaplasia was significantly greater than that in the vehicle controls, but was lower than that in the 200 ng/kg core study group. At 14-weeks, lung weights were significantly increased in the 200 ng/kg group compared to the vehicle controls. A single occurrence of a multiple cystic keratinizing epithelioma of the lung was observed in the 200 ng/kg core study group. There were increases in the incidences of bronchiolar metaplasia of the alveolar epithelium and sporadic incidences of squamous metaplasia. One pancreatic acinar adenoma and one pancreatic acinar carcinoma were each observed in the 92 ng/kg group and in the 200 ng/kg stop-exposure group at 2 years. Significantly increased incidences of acinar cytoplasmic vacuolization and arterial chronic active inflammation and increased severity of chronic active inflammation were observed in the 200 ng/kg core study group. Numerous nonneoplastic effects were seen in other organs including thyroid follicular cell hypertrophy, thymic atrophy, adrenal cortex cystic degeneration, nephropathy, cardiomyopathy, and squamous hyperplasia of the forestomach.
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PMID:Toxicology and carcinogenesis studies of 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) (Cas No. 57117-31-4) in female Harlan Sprague-Dawley rats (gavage studies). 1716 Jan 3

DIOXIN TOXIC EQUIVALENCY FACTOR EVALUATION OVERVIEW: Polyhalogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have the ability to bind to and activate the ligand-activated transcription factor, the aryl hydrocarbon receptor (AhR). Structurally related compounds that bind to the AhR and exhibit biological actions similar to TCDD are commonly referred to as "dioxin-like compounds" (DLCs). Ambient human exposure to DLCs occurs through the ingestion of foods containing residues of DLCs that bio-concentrate through the food chain. Due to their lipophilicity and persistence, once internalized they accumulate in body tissues, mainly adipose, resulting in chronic lifetime human exposure. Since human exposure to DLCs always occurs as a complex mixture, the toxic equivalency factor (TEF) methodology has been developed as a mathematical tool to assess the health risk posed by complex mixtures of these compounds. The TEF methodology is a relative potency scheme that ranks the dioxin-like activity of a compound relative to TCDD, the most potent congener. This allows for the estimation of the potential dioxin-like activity of a mixture of chemicals, based on a common mechanism of action involving an initial binding of DLCs to the AhR. The toxic equivalency of DLCs was nominated for evaluation because of the widespread human exposure to DLCs and the lack of data on the adequacy of the TEF methodology for predicting relative potency for cancer risk. To address this, the National Toxicology Program conducted a series of 2-year bioassays in female Harlan Sprague-Dawley rats to evaluate the chronic toxicity and carcinogenicity of DLCs and structurally related polychlorinated biphenyls (PCBs) and mixtures of these compounds. 2-YEAR STUDY: The 2-year study of a binary mixture of PCB 126 and PCB 153 was designed to assess the carcinogenicity of a constant ratio mixture of PCB 126 and PCB 153. In addition, varying ratio mixture groups were used to assess the impact of increasing PCB 153 on the carcinogenicity of PCB 126. Dose groups were divided into two study arms (Figure 1). TCDD equivalent (TEQ) doses are based on the PCB 126 doses after adjustment for the PCB 126 TEF of 0.1. Groups of 81 (Groups 2, 3, 5, and 7) or 80 (Groups 4 and 6) female rats received a mixture of PCB 126 and PCB 153 in corn oil:acetone (99:1) by gavage 5 days per week for up to 105 weeks; a group of 81 female rats received the corn oil:acetone (99:1) vehicle only and served as the vehicle control (Group 1). Up to 10 rats per group were evaluated at 14, 31, and 53 weeks. Survival of all dosed groups was similar to that of the vehicle controls. The mean body weights of Groups 4 and 5 were generally less than those of the vehicle controls after week 25. The mean body weights of Group 6 were less after week 12, and those of Group 7 were less after week 8. Thyroid Hormone Concentrations: Alterations in serum thyroid hormone levels were evaluated at the 14-, 31-, and 53-week interim evaluations. In the constant ratio groups, serum total thyroxine (T(4)) and free T(4) generally showed a treatment-related decrease relative to controls. Serum total triiodothyronine (T(3)) exhibited a treatment-related increase at the 14-, 31-, and 53-week interim evaluations, but serum thyroid stimulating hormone (TSH) levels were increased at the 14-week time point only. In the varying ratio groups, the decrease in total and free T(4) was more pronounced in those groups dosed with the increasing proportion of PCB 153 at the 31- and 53-week time points. Hepatic Cell Proliferation Data: To evaluate hepatocyte replication, analysis of labeling of replicating hepatocytes with 5-bromo-2'-deoxyuridine was conducted at the 14-, 31-, and 53-week interim evaluations. At 31 and 53 weeks, a significant increase in the hepatocellular labeling index occurred in Group 7. In the varying ratio groups, the labeling index at the 53-week interim time point was significantly higher in Group 6, which had the highest proportion of PCB 153 compared to the other varying ratio groups. Cytochrome P450 Enzyme Activities: To evaluate the expression of known PCB 126-responsive genes, CYP1A1-associated 7-ethoxyresorufin-O-deethylase (EROD) and CYP1A2-associated acetanilide-4-hydroxylase (A4H) activities were evaluated at the 14-, 31-, and 53-week interim evaluations. In addition, PCB 153-inducible CYP2B-associated 7-pent-oxyresorufin-O-dealkylase (PROD) activity was analyzed. In the constant ratio Groups 2, 3, 5, and 7, hepatic and pulmonary EROD (CYP1A1) activities, hepatic A4H (CYP1A2) activities, and hepatic PROD (CYP2B) activities were significantly greater in all dosed groups compared to the vehicle controls at weeks 14, 31, and 53. In the varying ratio groups, hepatic EROD, A4H, and PROD activities at 14 weeks were higher in groups receiving a greater proportion of PCB 153 in the PCB mixture. At 31 and 53 weeks, hepatic CYP1A1 and CYP1A2 enzyme activities in Group 6 were generally lower than in Groups 4 and 5. Determinations of PCB 126 and PCB 153 Concentrations in Tissues: Concentrations of PCB 126 and PCB 153 were determined in fat, liver, lung, and blood at the 14-, 31-, and 53-week interim evaluations and at the end of the 2-year study (105 weeks). PCB 126 was not detectable in vehicle control animals, but increased with increasing dose of PCB 126 and duration of exposure; the highest concentrations were found in liver and fat, and lower levels were seen in lung and blood. Increasing the proportion of PCB 153 in the mixture relative to PCB 126 led to a general decrease in the amount of PCB 126 in liver and lung at the later time points, whereas in fat and blood, there was generally either no effect of PCB 153 on the disposition of PCB 126, or there was an increase in the amount of PCB 126 in the tissue. In vehicle control animals, PCB 153 was detectable in the fat at all time points, in the lung at all time points except 53 weeks, and in the liver and blood at 2 years. PCB 153 was measurable in all examined tissues of treated animals, with the highest concentrations found in fat at the end of the 2-year study in groups administered the highest doses of PCB 153. Pathology and Statistical Analyses -- Constant Ratio Mixture of PCB 126 and PCB 153: At 14, 31, and 53 weeks, the absolute and relative liver weights of all dosed groups were generally greater than those of the vehicle controls. Exposure to the PCB mixture led to significant toxicity in the liver. At 14 weeks, the incidences of several nonneoplastic liver lesions were increased compared to the vehicle controls including hepatocyte hypertrophy, pigmentation, multinucleated hepatocytes, and diffuse fatty change. The spectrum and severity of effects increased with dose and duration of exposure. At the end of the 2-year study, there were significantly increased incidences and severities of toxic hepatopathy characterized by hepatocyte hypertrophy, multinucleated hepatocytes, pigmentation, diffuse and focal fatty change, eosinophilic focus, nodular hyperplasia, cholangiofibrosis, oval cell hyperplasia, bile duct cysts, bile duct hyperplasia, necrosis, and portal fibrosis. Significantly increased incidences of hepatocellular adenoma, cholangiocarcinoma, and hepatocholangioma were observed in the study. In addition, two animals in the highest dose group had hepatocellular carcinoma. The incidences of these lesions generally exceeded the historical vehicle control ranges. At 2 years, a significantly increased incidence of cystic keratinizing epithelioma of the lung was observed in Group 7. In addition, single occurrences of squamous cell carcinoma were seen in the top two dose groups. Nonneoplastic effects whose incidences were increased in the lung included bronchiolar metaplasia of the alveolar epithelium and squamous metaplasia. Significantly increased incidences of squamous cell carcinoma (gingival) of the oral mucosa were seen at the end of the 2-year study and were accompanied by increased incidences of gingival squamous hyperplasia. In the pancreas at 53 weeks, the incidence of acinar cytoplasmic vacuolization was significantly increased in the highest dose group. At 2 years, increased incidences of acinar atrophy and acinar cytoplasmic vacuolization were seen in addition to pancreatic acinar neoplasms in dosed groups. In Groups 5 and 7, these incidences exceeded the historical vehicle control ranges. In the uterus at 2 years, there was a marginal increase in the incidence of squamous cell carcinoma in Group 5. Numerous nonneoplastic effects were seen in other organs at the interim time points including atrophy of the thymus and follicular cell hypertrophy of the thyroid gland. These responses were also affected by administration of the mixture of PCB 126 and PCB 153 at the end of the 2-year study and were accompanied by additional nonneoplastic responses in numerous organs including atrophy of the adrenal cortex and cortical hyperplasia, severity of nephropathy, and incidences of pigmentation of the kidney. Other nonneoplastic lesions that were treatment related were forestomach hyperplasia, hyperplasia of the nasal respiratory epithelium, metaplasia of the olfactory epithelium, and ectasia of the mandibular lymph node. Varying Ratio Mixture of PCB 126 and PCB 153: An effect of increasing the proportion of PCB 153 in the PCB mixture was seen in several tissues, most notably in the liver. Treatment-related nonneoplastic effects seen across the varying ratio groups were generally the same as those seen in the constant ratio groups. In general there was a positive effect of PCB 153 in the mixture on the incidences and severities of these lesions with higher incidences and higher severities being seen in Group 6, which had the highest proportion of PCB 153. (ABSTRACT TRUNCATED).
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PMID:Toxicology and carcinogenesis studies of a binary mixture of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) (Cas No. 57465-28-8) and 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) (CAS No. 35065-27-1) in female Harlan Sprague-Dawley rats (gavage studies). 1716 Jan 4

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