Factors influencing the growth of normal and neoplastic thyroid tissue

Association between exposure to radioactive iodine after the Chernobyl accident and thyroid volume in Belarus 10-15 years later

BACKGROUND

While there is a robust literature on environmental exposure to iodine-131 (131I) in childhood and adolescence and the risk of thyroid cancer and benign nodules, little is known about its effects on thyroid volume.

METHODS

To assess the effect of 131I dose to the thyroid on the volume of the thyroid gland, we examined the data from the baseline screening of the Belarusian-American Cohort Study of residents of Belarus who were exposed to the Chernobyl fallout at ages ≤18 years. Thyroid dose estimates were based on individual thyroid activity measurements made shortly after the accident and dosimetric data from questionnaires obtained 10-15 years later at baseline screening. During baseline screening, thyroid gland volume was assessed from thyroid ultrasound measurements. The association between radiation dose and thyroid volume was modeled using linear regression where radiation dose was expressed with power terms to address non-linearity. The model was adjusted for attained age, sex, and place of residence, and their modifying effects were examined.

RESULTS

The analysis was based on 10,703 subjects. We found a statistically significant positive association between radiation dose and thyroid volume (P < 0.001). Heterogeneity of association was observed by attained age (P < 0.001) with statistically significant association remaining only in the subgroup of ≥18 years at screening (P < 0.001). For this group, increase in dose from 0.0005 to 0.15 Gy was associated with a 1.27 ml (95% CI: 0.46, 2.07) increase in thyroid volume. The estimated effect did not change with increasing doses above 0.15 Gy.

CONCLUSIONS

This is the first study to examine the association between 131I dose to the thyroid gland and thyroid volume in a population of individuals exposed during childhood and systematically screened 10-15 years later. It provides evidence for a moderate statistically significant increase in thyroid volume among those who were ≥ 18 years at screening. Given that this effect was observed at very low doses and was restricted to a narrow dose range, further studies are necessary to better understand the effect.

Is gender difference in postnatal thyroid growth associated with specific expression patterns of androgen and estrogen receptors?

Variations in sex steroids bioavailability were linked to the gender difference in the growth of thyroid glands of neonatal rats. In the present study we tested androgen receptor (AR) and estrogen receptor (ER) concentrations by ligand binding assay, and expression of their genes by RT-PCR and Western blot in the thyroid glands of neonatal rats. AR concentration remained elevated from postnatal day (PND) 10 onwards in males, whereas it decreased by PND 20 in females. AR mRNA and protein expressions were higher in males than females, which increased by PND 10, decreased after PND 15 and reached the nadir by PND 20. ER concentration increased by PND 10 and decreased thereafter in both sex. ERα mRNA expression diminished by PND 15 in both sex; while ERβ mRNA decreased by PND 15 to reach the nadir by PND 20 in males, it was augmented by PND 10 in females to reach the peak by PND 15 and diminished by PND 20. ERα protein expression increased by PND 10 and remained elevated till PND 20 in both sex. ERβ protein expression in males increased by PND 10 and decreased by PND 20, while it remained static up to PND 15 and decreased in females. Testosterone stimulated [(3)H]-thymidine uptake and the expression of IGF-1 and NIS genes in thyrocytes of both sex in vitro, while estradiol stimulated them in females but not in males. We conclude that androgens influence the growth and differentiation of thyrocytes through augmented expression of AR, IGF-1 and NIS in either sex, whereas estrogen imparts the gender difference, which may be at a level beyond the expression of ERs.

Expression, regulation and function of autotaxin in thyroid carcinomas

Autotaxin (ATX/NPP2) is a tumor cell motility-stimulating factor that displays both a nucleotide pyrophosphatase/phosphodiesterase activity and a recently described lysophospholipase D (lysoPLD) activity. The precise function of ATX in tumor cells and the role of ATX in thyroid carcinoma remains unclear. We have quantified ATX mRNA expression in thyroid carcinoma cell lines and in tissues of patients with thyroid carcinomas. ATX gene activity was significantly higher in undifferentiated anaplastic thyroid carcinoma cell lines (UTC) and tumor tissues as compared to follicular thyroid carcinoma (FTC) cell lines, FTC tissues or goiter tissues that were used as a control. In the thyroid carcinoma cell line 1736, EGF and bFGF stimulated ATX mRNA expression, whereas the cytokines IL-4, IL-1beta and TGF-beta reduced ATX transcriptional levels. FTC-133 cells, stably transfected with an expression vector for ATX, showed a higher lysoPLD activity, a higher proliferation rate and an increased migratory behavior. In addition, ATX also displayed a paracrine stimulatory effect on the motility of different thyroid carcinoma cell lines. Overexpression of ATX in the stably transfected FTC-133 resulted in down-regulation of CD54/ intercellular adhesion molecule-1 (ICAM-1) gene expression and augmented gene activity of the pro-angiogenic chemokine IL-8. We conclude that ATX may be regarded as a new tissue marker for undifferentiated human thyroid carcinoma cells. ATX increases the proliferation and migration of thyroid carcinoma cell lines and may also affect the angiogenic potential of thyroid carcinoma cells. Further studies are needed to provide insight into the role of ATX in the normal and neoplastic thyroid gland.

Juvenile hyperthyroidism in a cat

An 8-month-old, male domestic shorthaired cat presented for chronic weight loss, intermittent dyspnea, chronic diarrhea, hyperactivity, and weakness. The cat had a palpable thyroid nodule and increased serum total thyroxine and 3,5,3' triiodothyronine levels. The cat was diagnosed with hyperthyroidism, and a unilateral thyroidectomy was performed followed by radioactive iodine at a later date. The clinical signs resolved following radioactive iodine, and the cat subsequently developed clinical hypothyroidism.

Binding of a human monoclonal antithyroglobulin antibody to cultured human thyroid cancer cells

To develop a new method of radioimmunodetection for thyroid cancer, we tested the binding ability of a human antithyroglobulin monoclonal antibody, VB5, to primary culture of human thyroid cancer cells. VB5 was able to immunostain cytoplasmic thyroglobulin (Tg) in the acetone-fixed cancer cells when used in a labeled streptavidin-biotin method but not in a conventional indirect immunoperoxidase technique. The antibody was readily labeled with I-125 in the standard chloramin-T method, and showed specific binding to the antigen on cultured malignant thyrocytes displaceable with non-labeled VB5 or with excess Tg antigen. Although these initial results in vitro are encouraging, the observed low specific binding (about 1% at room temperature) to intact cells with a single monoclonal antibody seems insufficient to conduct any in vivo immunolocalization experiments in animals. To obtain more binding, we would need a cocktail of several monoclonal antibodies to different epitopes, and also fragmentation of antibody molecules to penetrate into cytoplasm.

Thyroid growth factors, signal transduction pathways, and oncogenes

Growth of thyroid cancer cells is stimulated by various growth factors via signal transduction pathways. TSH, EGF, IGF, and TGF-alpha stimulate and TGF-beta inhibits thyroid cell growth. TSH stimulates thyroid cells via both the adenylate cyclase-PKA and the PLC-PKC-Ca signal transduction pathways. TSH-r, ras, gsp, ret, trk, and myc are oncogenes that are activated in some thyroid neoplasms. P53 and RB are tumor suppressor genes that are inactivated in some thyroid cancers.

Etiopathology of feline toxic nodular goiter

We have discussed the etiopathology of feline toxic nodular goiter in the context of human nodular goiter pathogenesis. We have reviewed thyroid heterogeneity, growth regulation, functional and growth autonomy, nodule and tumor formation, and the evolution of toxic nodular goiter in the human being. By addressing toxic nodular goiter of the cat, the history, morphologic findings, xenotransplantation and cell culture studies, evidence for and against circulating thyroid stimulators and epizootiological studies of the feline disease have been summarized. Due to its structure, the thyroid gland offers some unique possibilities to study the mechanisms that are responsible for cellular heterogeneity, the emergence of autonomous nodular growth and function, and, ultimately, the development of tumors. The demonstration of naturally occurring clones of cells with high intrinsic proliferation potential within the follicular epithelium of the thyroid has fostered promising new concepts on the genesis of nodular growth of benign and possibly malignant endocrine tumors. Hyperthyroid cat goiters contain single or multiple, autonomously (i.e., TSH-independently) functioning and growing nodules. Neither hyperfunction nor growth of these nodules depends on extrathyroidal circulating stimulators. The basic lesion appears to be an excessive intrinsic growth capacity of some thyroid cells. The factors enhancing the transformation of a normal thyroid into a nodular hyperfunctioning goiter over many years are still unknown. Immunological, environmental, and nutritional factors are the focus of ongoing studies, but an infectious agent can not yet be excluded.

Rapidly growing thyroid carcinoma during pregnancy

We experienced two cases of papillary carcinoma of the thyroid during pregnancy. The thyroid carcinomas grew rapidly in early pregnancy. We speculate that human chorionic gonadotropin plays an important role in the rapid growth of thyroid carcinoma during pregnancy.

Diagnosis, treatment, and outcome of follicular thyroid carcinoma

BACKGROUND

There have been numerous studies concerning the diagnosis, treatment, and prognosis of patients with papillary thyroid carcinoma, but relatively few addressing patients with follicular carcinoma.

METHODS

The authors analyzed their experience with 65 patients who underwent 96 thyroid operations for pure follicular thyroid carcinoma from 1956 to 1990.

RESULTS

The patients were 43 women and 22 men with a mean age of 45 years who were followed postoperatively for a mean of 10.4 years. Fifty-two patients (80%) were seen initially with a solitary thyroid nodule, and 24 (37%) had symptoms at presentation. Median tumor size was 2.2 cm. Fine-needle aspiration biopsy was performed in 20 patients, revealing a follicular neoplasm in 18 patients (90%) and an inadequate specimen in 2 patients. Nineteen patients received thyroid-stimulating hormone (TSH)-suppressive thyroid hormone therapy for an average of 4.5 months before surgery; tumor size remained the same in 10 patients (53%), increased in 5 (26%), and decreased in 2 (11%). At presentation, six patients had lymph node involvement, three had locally invasive tumors, and two had distant metastases. Initial operative treatment was lobectomy in 32 patients (49%), total thyroidectomy in 15 patients (23%), lobectomy plus contralateral partial or subtotal lobectomy in 11 patients (17%), and lesser procedures in 7 patients (11%). Twenty-nine patients had a completion total thyroidectomy, so that final surgical treatment consisted of total thyroidectomy in 44 patients (68%). Among 39 patients having intraoperative frozen section, only 3 (8%) were correctly diagnosed as having cancer. Permanent complications occurred during 3 of the 96 operations. Three patients (5%) have died of thyroid cancer (one with anaplastic transformation) since thyroidectomy, and two are living with distant metastatic disease.

CONCLUSIONS

Patients with follicular thyroid cancer, when first examined, usually have solitary thyroid nodules that are follicular neoplasms by aspiration cytology, and these nodules fail to regress in response to TSH-suppressive therapy. Frozen section rarely aids in management. The preferred treatment for follicular neoplasms is lobectomy followed by completion total thyroidectomy for histologically proven carcinomas larger than 1.0 cm. Total thyroidectomy allows use of thyroglobulin and radioiodine scanning to detect and treat metastatic disease. Complications of thyroidectomy were uncommon, and the mortality rate in treated patients was relatively low.

Cholecalciferol metabolites attenuate cAMP production in rat thyroid cells (FRTL-5)

A rat thyroid cell line (FRTL-5) was used to study the effect of cholecalciferols on cAMP production. The active cholecalciferol metabolite, calcitriol, caused a reduction in basal and thyrotropin (TSH)-stimulated cAMP production. The inhibitory effects were demonstrated after 1 and 2 days, respectively. The maximum effect on both basal and TSH-stimulated cAMP production was observed after 3-4 days of treatment. The effect was detectable at 10(-10) and maximal at 10(-8) mol/l. Calcitriol was about 300 times more potent than calcidiol in attenuating cAMP production, whereas (24R)-hydroxycalcidiol in concentrations up to 3 x 10(-8) mol/l had no effect. After removal of added calcitriol the cAMP response to TSH returned to normal within 8 days. Calcitriol (10(-8) mol/l) also inhibited cell growth. Our results show that calcitriol at physiological concentrations inhibits both basal and TSH-stimulated cAMP production in rat thyroid cells. This indicates that calcitriol may modulate the effect of TSH on thyroid function and growth.

Role of thyroid stimulating hormone suppression in the management of thyroid cancer

Well-differentiated thyroid cancers (papillary, follicular, and some Hurthle cell tumors) contain membrane receptors for TSH. Responsiveness of these tumors to TSH stimuli is documented by increased radioactive iodine uptake, secretion of thyroglobulin, increase in thyroid size, and potential progression to an anaplastic type. Although TSH suppression has a variable effect on the growth of existing tumors and the incidence of recurrent disease, there is a sound rationale for long-term TSH suppression in all patients with differentiated tumors of the thyroid. The ultrasensitive TSH test permits ready monitoring of the adequacy of thyroxine dosage. The cost is minimal (approximately $.10/day) and the risks are negligible if one assumes the avoidance of hyperthyroxinemia.

Epidermal growth factor receptors and adenylate cyclase activity in human thyroid tissues

Thyroid stimulating hormone (TSH) and epidermal growth factor (EGF) are growth factors for some thyroid cells in cultures. We have previously found more EGF receptors in neoplastic human thyroid tissues than in normal thyroid tissues. We have also found a higher TSH-stimulated adenylate cyclase (AC) activity in neoplastic human thyroid tissues than in normal thyroid tissues. To clarify the relationship between the effect of EGF and TSH on thyroid tissue, we measured the binding of EGF and TSH and the basal, TSH-stimulated and forskolin-stimulated adenylate cyclase activity in 49 normal, hyperplastic and neoplastic human thyroid tissues (5 normal, 2 Hashimoto thyroiditis, 5 Graves' disease, 14 multinodular goiters, 9 follicular adenomas, 5 follicular carcinomas, 8 papillary carcinomas, and 1 undifferentiated carcinoma). Specific binding of EGF and TSH were measured by radioreceptor assays using competitive inhibition of radio-labeled ligand by unlabeled ligand. Basal, maximally (300 mU/ml) TSH-stimulated, and maximally (100 mM) forskolin-stimulated adenylate cyclase activities were also measured in the same membrane particulate fractions from the thyroid tissues. We found: neoplastic thyroid tissues bind more labeled EGF than nonneoplastic thyroid tissues; follicular adenomas and carcinomas have higher EGF binding than other thyroid tissues; a weak but significant correlation between specific EGF binding and specific TSH binding, and between specific EGF binding and TSH-stimulated adenylate cyclase activity of the thyroid membrane preparations. These findings are consistent with the hypothesis that TSH stimulates an increase in thyroid EGF receptors by increasing intracellular cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)