Hypertrophy Of Follicular Epithelial Cells Research Articles

Dietary selenium promotes the growth performance through growth hormone-insulin-like growth factor and hypothalamic-pituitary-thyroid axes in grass carp (Ctenopharyngodon idella).

Selenium (Se), an essential component of deiodinases (DIOs), regulates the contents of thyroid hormones and thus improves animal growth. To explore the influences of selenium supplementation on fish growth metabolism, a total of 270 healthy grass carp (Ctenopharyngodon idella) were divided into three groups and feed three graded dietary selenium (0.141, 0.562, and 1.044mg Se/kg) levels. The results showed that after 60-day feeding, dietary selenium improved the final body weight and specific growth rate (SGR) of grass carp. The hepatic DIO activities in selenium-supplemented groups were higher than those in control group. A significant increase in triiodothyronine (T3), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) levels was accompanied by a decrease in the contents of thyroxine (T4) and free thyroxine (FT4) in selenium-supplemented groups. The histopathological observation of thyroid suggested that selenium deficiency resulted in hypertrophy of follicular epithelial cells. Moreover, the gene relative expression levels of dio1, dio2, and dio3 showed an increasing trend with the rising concentration of dietary selenium. The transcription levels of HPT axis-related genes (crh, tsh-β, ttr, tr-s, tpo, nis) and GH/IGF1-related genes (gh, ghr, igf1, igf1r) were significantly upregulated in selenium-supplemented groups. No significant differences in the above indicators were observed between 0.562 and 1.044mg Se/kg diet group except T3 content and dio1 relative expression ratio. These results indicate that dietary selenium supplementation improves the hepatic DIO activities and thyroid hormone metabolism and regulates the transcription levels of HPT and GH/IGF axis-related genes, which may be responsible for the growth promotion in grass carp.

Flubenziamide (Pesticides).

The Food Safety Commission of Japan (FSCJ) conducted a risk assessment of flubendiamide (CAS No. 272451-65-7), an iodophthalimide insecticide for the setting of an acceptable daily intake (ADI) in 2006. FSCJ now has assessed this insecticide for the setting of an acute reference dose (ARfD). Data including fate in animals (rats and mice) and residues in crops (burdock roots, pumpkins and others) were newly submitted. Major adverse effects of flubendiamide include hepatocellular hypertrophy, fatty changes in hepatocytes, follicular epithelial cell hypertrophy in thyroid and ocular enlarged eye in rats. No neurotoxicity, carcinogenicity, reproductive toxicity, teratogenicity, neurodevelopmental toxicity and genotoxicity were observed. The lowest no-observed-adverse-effect level (NOAEL) in the toxicological studies was 1.70 mg/kg body weight/day in a two-year carcinogenicity study in rats. FSCJ confirmed an ADI of 0.017 mg/kg bw/day after applying a safety factor of 100 to the NOAEL. Adverse effects elicited by a single oral administration of flubendiamide would be abnormalities in eyes such as ocular hypertrophy and iris adhesion in offspring, which were obtained in a two-generation reproductive toxicity study, a one-generation reproductive toxicity study and a neurodevelopmental toxicity study in rats. FSCJ judged that these studies may be applicable to set the ARfD for lactating women in relation to the exposure of flubendiamide to offspring after the birth through breast milk. By taking into account the overall evaluations of the two-generation reproductive toxicity study, one-generation reproductive toxicity study and neurodevelopmental toxicity study in rats, FSCJ judged NOAEL of 15.0 mg/kg bw/day as for an overall NOAEL, and consequently specified an ARfD of 0.15 mg/kg bw/day for lactating women by applying a safety factor of 100 to the NOAEL.

Flubenziamide (Pesticides)

The Food Safety Commission of Japan (FSCJ) conducted a risk assessment of flubendiamide (CAS No. 272451-65-7), an iodophthalimide insecticide for the setting of an acceptable daily intake (ADI) in 2006. FSCJ now has assessed this insecticide for the setting of an acute reference dose (ARfD). Data including fate in animals (rats and mice) and residues in crops (burdock roots, pumpkins and others) were newly submitted. Major adverse effects of flubendiamide include hepatocellular hypertrophy, fatty changes in hepatocytes, follicular epithelial cell hypertrophy in thyroid and ocular enlarged eye in rats. No neurotoxicity, carcinogenicity, reproductive toxicity, teratogenicity, neurodevelopmental toxicity and genotoxicity were observed. The lowest no-observed-adverse-effect level (NOAEL) in the toxicological studies was 1.70 mg/kg body weight/day in a two-year carcinogenicity study in rats. FSCJ confirmed an ADI of 0.017 mg/kg bw/day after applying a safety factor of 100 to the NOAEL. Adverse effects elicited by a single oral administration of flubendiamide would be abnormalities in eyes such as ocular hypertrophy and iris adhesion in offspring, which were obtained in a two-generation reproductive toxicity study, a one-generation reproductive toxicity study and a neurodevelopmental toxicity study in rats. FSCJ judged that these studies may be applicable to set the ARfD for lactating women in relation to the exposure of flubendiamide to offspring after the birth through breast milk. By taking into account the overall evaluations of the two-generation reproductive toxicity study, one-generation reproductive toxicity study and neurodevelopmental toxicity study in rats, FSCJ judged NOAEL of 15.0 mg/kg bw/day as for an overall NOAEL, and consequently specified an ARfD of 0.15 mg/kg bw/day for lactating women by applying a safety factor of 100 to the NOAEL.

Cyclaniliprole (Pesticides).

The Food Safety Commission of Japan (FSCJ) conducted a risk assessment of cyclaniliprole (CAS No. 1031756-98-5), an anthranilamide insecticide, based on results from various studies. Major treatment-related effects of cyclaniliprole were observed on liver (increased liver weight and increased alkaline phosphatase) in dogs and on thyroid (hypertrophy of follicular epithelial cells) in rats. None of neurotoxicity, carcinogenicity, reproductive toxicity, teratogenicity, immunotoxicity and genotoxicity were observed. Based on the results from various studies, only parent cyclaniliprole was identified as the relevant substance to the residue definition for dietary risk assessment in agricultural products. The lowest no-observed-adverse-effect level (NOAEL) obtained in all the toxicity studies was 1.29 mg/kg bw/day in a one-year chronic toxicity study in dogs. FSCJ has established an acceptable daily intake (ADI) of 0.012 mg/kg bw/day, by applying a safety factor of 100 to the NOAEL. FSCJ judged it unnecessary to specify an acute reference dose (ARfD) since no adverse effects, possibly elicited by a single oral administration, was observed.

Picarbutrazox (Pesticides).

The Food Safety Commission of Japan (FSCJ) conducted a risk assessment of picarbutrazox (CAS No.500207-04-5), a methyltetrazole-type fungicide, based on results from various studies. Major adverse effects of picarbutrazox were observed as hepatocellular hypertrophy and hypertrophy of follicular epithelial cells in rats. None of neurotoxicity, reproductive toxicity, teratogenicity and genotoxicity were detected in the experiments described above. Picarbutrazox (parent compound only) and its metabolite B were identified as the relevant substance for the residue definition for dietary risk assessment in agricultural products. The lowest no-observed-adverse-effect level (NOAEL) obtained in all studies was 2.34 mg/kg bw/day in a two-year combined chronic toxicity/carcinogenicity study in rats. FSCJ specified an acceptable daily intake (ADI) of 0.023 mg/kg bw/day, applying a safety factor of 100 to the NOAEL. FSCJ judged it unnecessary to specify an acute reference dose (ARfD), since no adverse effects would be likely to be elicited by a single oral administration.

DEHP reduces thyroid hormones via interacting with hormone synthesis-related proteins, deiodinases, transthyretin, receptors, and hepatic enzymes in rats.

Di-(2-ethylhexyl) phthalate (DEHP) is used extensively in many personal care and consumer products, resulting in widespread nonoccupational human exposure through multiple routes and media. Limited studies suggest that exposure to DEHP may be associated with altered thyroid function, but detailed mechanisms are unclear. In order to elucidate potential mechanisms by which DEHP disturbs thyroid hormone homeostasis, Sprague-Dawley (SD) rats were dosed with DEHP by gavage at 0, 250, 500, and 750 mg/kg/day for 30 days and sacrificed within 24 h after the last dose. Gene expressions of thyroid hormone receptors, deiodinases, transthyretin, and hepatic enzymes were measured by RT-PCR; protein levels of transthyretin were also analyzed by Western blot. Results showed that DEHP caused histological changes in the thyroid and follicular epithelial cell hypertrophy and hyperplasia were observed. DEHP significantly reduced thyroid hormones (T3, T4) and thyrotropin releasing hormone (TRH) levels, whereas thyroid stimulating hormone (TSH) was not affected. After exposure to DEHP, biosynthesis of thyroid hormones was suppressed, and sodium iodide symporter (NIS) and thyroid peroxidase (TPO) levels were significantly reduced. Additionally, levels of deiodinases and transthyretin were also affected. TSH receptor (TSHr) level was downregulated, while TRH receptor (TRHr) level was upregulated. Metabolism of thyroid hormones was accelerated due to elevated gene expression of hepatic enzymes (UDPGTs and CYP2B1) by DEHP. Taken together, observed findings indicate that DEHP could reduce thyroid hormones through influencing biosynthesis, biotransformation, biotransport, receptor levels, and metabolism of thyroid hormones.

Uterotrophic assay, Hershberger assay, and subacute oral toxicity study of 3-amino-1,2,4-triazole based on the Organization for Economic Co-operation and Development draft protocols

We performed a uterotrophic assay, the Hershberger assay, and the 28-day repeated-dose toxicity study (enhanced OECD test guideline no. 407) of 3-amino-1,2,4-triazole based on the OECD draft protocols. In the uterotrophic assay, female SD rats were subcutaneously injected with the chemical at doses of 0, 100, 300, and 1,000 mg/kg on each of 3 days from postnatal day 20 to day 22, and no changes were observed. In the Hershberger assay, the test chemical was orally administered at doses of 0, 40, 200, and 1,000 mg/kg/day to castrated male Wistar rats for 10 consecutive days beginning on postnatal day 56, and no androgen agonistic and antagonistic changes were observed. Alternatively, when the test chemical was orally administered at doses 0, 5, 25, and 125 mg/kg/day for at least 28 days in the subacute oral toxicity study, thyroid follicular epithelial cell hypertrophy with increased thyroid weights was detected in the male and female rats in 25 and/or 125 mg/kg groups, and hypertrophy of the anterior pituitary cells with increased pituitary weights in male and female rats was also observed in the 125 mg/kg group. Furthermore, serum T3 and T4 values decreased and serum TSH values increased in male and female rats in the 125 mg/kg group. Therefore, 3-amino-1,2,4-triazole was concluded to have anti-thyroid acting as endocrine-mediated effects, but no estrogenic or androgenic effects. In addition, decreased body weight, and abnormal biochemical parameters attributed to thyroid, liver or kidney dysfunction were observed in male and female rats in the 25 and/or 125 mg/kg groups.

Uterotrophic assay, Hershberger assay, and subacute oral toxicity study of 4,4′-butylidenebis(2-tert-butyl-5-methylphenol) and 3-(dibutylamino)phenol, based on the OECD draft protocols

We performed a uterotrophic assay, the Hershberger assay, and a 28-day repeated-dose toxicity study [enhanced Organization for Economic Co-operation and Development (OECD) test guideline No. 407] of 4,4'-butylidenebis(2-tert-butyl-5-methylphenol) and 3-(dibutylamino)phenol, based on the OECD draft protocols. In the uterotrophic assay of 4,4'-butylidenebis(2-tert-butyl-5-methylphenol), female SD rats were subcutaneously injected with the chemical at doses of 0, 100, 300, and 1,000 mg/kg on each of 3 days from postnatal day 20 to day 22, and no changes were observed. In the Hershberger assay of 4,4'-butylidenebis(2-tert-butyl-5-methylphenol), the test chemical was orally administered to castrated male SD rats at doses of 0, 50, 200, and 1,000 mg/kg/day for ten consecutive days beginning on postnatal day 56, and no changes were observed. When this chemical was orally administered at doses 0, 5, 25, and 125 mg/kg/day for at least 28 days in the subacute oral toxicity study, an increase in thyroid weight was observed in the female rats in the 125 mg/kg group, an increase in serum thyroid-stimulating hormone (TSH) values in the male and female rats in the 125 mg/kg group, and a decrease in serum T3 and T4 values in the male rats in the 125 mg/kg group, and thyroid follicular epithelial cell hypertrophy was observed in some of the female rats in the 125 mg/kg group. These findings were concluded to be the result of endocrine-mediated effects of the chemical on thyroid function. In addition, increased liver weight, abnormal histological findings in the liver, and abnormal biochemical parameters related to liver function were observed in male and/or female rats in 5 mg/kg group and higher dose groups. The no-observed-effect level for 4,4'-butylidenebis(2-tert-butyl-5-methylphenol) was concluded to be <5 mg/kg/day. In the uterotrophic assay of 3-(dibutylamino)phenol, female SD rats were subcutaneously injected with the chemical at doses of 0, 100, 300, and 1,000 mg/kg on each of 3 days from postnatal day 20 to day 22, and no changes were observed. In the Hershberger assay of 3-(dibutylamino)phenol, the test chemical was orally administered at doses of 0, 50, 200, and 400 mg/kg/day to castrated male SD rats for ten consecutive days beginning on postnatal day 56, and no changes were observed. On the other hand, when this test chemical was orally administered at doses 0, 30, 100, and 300 mg/kg/day for at least 28 days in the subacute oral toxicity study, thyroid weight increased in the male rats in the 300 mg/kg group, thyroid follicular epithelial cell hypertrophy was observed in a small number of male rats in the 300 mg/kg group, serum T3-values decreased in the female rats in the 300 mg/kg group, and a tendency for TSH-values to increase was observed in the male and female rats in the 300 mg/kg group. Therefore, 3-(dibutylamino)phenol was also concluded to have slight anti-thyroid acting effects as the endocrine-mediated effects. On the other hand, increased hemosiderin deposition in the spleen, increased spleen weight, hematological abnormalities, and squamous epithelial hyperplasia of the forestomach were detected in male and/or female rats in the 100 and/or 300 mg/kg groups, and thus the no-observed-effect level for 3-(dibutylamino)phenol was concluded to be 30 mg/kg/day.

A Mixture of Ammonium Perchlorate and Sodium Chlorate Enhances Alterations of the Pitutary-Thyroid Axis Caused by the Individual Chemicals in Adult Male F344 Rats

Ammonium perchlorate (AP) and sodium chlorate (SC) have been detected in public drinking water supplies in many parts of the United States. These chemicals cause perturbations in pituitary-thyroid homeostasis in animals by competitively inhibiting iodide uptake, thus hindering the synthesis of thyroglobulin and reducing circulating T(4) (thyroxine). Little is known about the short-term exposure effects of mixtures of perchlorate and chlorate. The present study investigated the potential for the response to a mixture of these chemicals on the pituitary-thyroid axis in rats to be greater than that induced by the individual chemicals. Adult male F-344 rats were exposed, via their drinking water, to the nominal concentrations of 0.1, 1.0, 10 mg/L AP or 10, 100, 1000 mg/L SC and their mixtures for 7 days. Serum T(4) levels were significantly (p < 0.05) reduced in rats following exposure to the mixtures, but not after exposure to the individual chemicals. Serum T(3) (triiodothyronine) was not altered by treatment and TSH (thyroid stimulating hormone) was only increased after the high-dose chlorate treatment. Histological examination of the thyroid gland showed colloid depletion and hypertrophy of follicular epithelial cells in high-dose single chemical and all mixture-treated rats, while hyperplasia was observed only in some of the rats treated with mixtures (AP 10 + SC 100, AP 0.1 + SC 1000, and AP 10 + SC 1000 mg/L). These data suggest that short-term exposure to the mixture of AP and SC enhances the effect of either chemical alone on the pituitary-thyroid axis in rats.

Follicular epithelial cell hypertrophy induced by chronic oral administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin in female Harlan Sprague-Dawley rats.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) affects the thyroid morphologically and/or functionally in adult animals. Recently, the National Toxicology Program conducted a 2-year gavage study of TCDD in female Harlan Sprague-Dawley rats. The only treatment-related alterations found in thyroid follicles were decreased luminal size and increased height of the follicular epithelial cells, without prominent protrusion into the lumen. The present study elucidated the nature of these follicular lesions. Thyroid glands of 10 rats each from the control, high (100 ng/kg/day)-dose, and stop-study (100 ng/kg/day, 30 weeks; vehicle to study termination) groups in the 2-year study were evaluated microscopically. Twenty randomly selected follicles were measured morphometrically in each animal. TCDD treatment significantly decreased the mean ratio of luminal/epithelial areas and increased the mean sectional epithelial height of the high-dose group compared to controls. Thyroid sections were immunostained with antibody against minichromosome maintenance (MCM) proteins, a novel cell-cycle biomarker. The MCM labeling index of the high-dose group was significantly higher than that of the control; however, the TUNEL labeling index was also higher in the high-dose group than the control. All data from the stop group were comparable to those from controls. These results indicate that the follicular cell response was hypertrophic and reversible. This information should contribute to diagnosis of nonneoplastic thyroid follicular lesions in rats.

Thyroid hyperactivity induced by methimazole, spironolactone and phenobarbital in marmosets (Callithrix jacchus): histopathology, plasma thyroid hormone levels and hepatic T4 metabolism.

To determine drug-induced hyperfunction of marmoset thyroids due to inhibition of synthesis or enhancement of metabolic elimination of thyroid hormones, males were orally administered 10 and 30 mg/kg/day methimazole (MMI), 30 and 100 mg/kg/day spironolactone (SPL), or 50 mg/kg/day phenobarbital (PB) for 4 weeks. MMI caused marked hypertrophy of follicular epithelial cells in accordance with a significant decrease in the plasma thyroxin (T4) level. Hypertrophied epithelial cells were filled with dilated rough endoplasmic reticulum and reabsorbed intracellular colloids, and the luminal surface was covered with abundant microvilli. The colloid included vacuoles positive to anti T4 immuno-staining. SPL and PB also caused similar histomorphological changes, although they were less severe than those due to MMI and were not clearly associated with decrease in the plasma T4 levels. Hepatic T4 UDPGT activities tended to increase due to SPL and PB treatment, however, which were not so significant as increases in microsomal cytochrome P-450 contents. Some animals treated with SPL and PB showed marked increases in thyroid weights due to inactive dilated follicles. In conclusion, hyperactivity of thyroid follicles was induced in marmosets not only due to inhibition of T4 synthesis produced by MMI but also because of enhancement of hepatic T4 elimination produced by SPL and PB. However, hypertrophic effects of SPL and PB were less severe than MMI, because plasma T4 levels were maintained at almost pretreatment or control levels after SPL or PB treatment.

The effect of prolonged Kale feeding on the thyroid glands of sheep

Four groups of sheep were fed the following rations: Group I Kale ad lib., Group II Kale ad lib.+0·22 kg. blood meal/flaked maize mixture, Group III Kale ad lib.+0·22 kg. blood meal/flaked maize mixture and 10 mg. Kl weekly by mouth, Group IV 0·9 kg. hay+0·22 kg. blood meal/flaked maize mixture. They were fed these rations for 17 weeks when the sheep were killed. The thyroids were removed, weighed and pieces were taken for histological examination. The kale had a goitrogenic effect which was overcome by the iodine supplementation. The group receiving kale showed only a three-fold increase in thyroid weight whereas the group receiving the blood meal/flaked maize mixture in addition to the kale showed a six-fold increase in weight. The mixture had no goitrogenic effect when fed without kale to the control group. The mixture appears to increase the goitrogenicity of the kale. The histology shows considerable hypertrophy of follicular epithelial cells and a diminution in colloid and this accounts for the weight incrase of the glands.