2-Methoxyestradiol, an endogenous estrogen metabolite, induces thyroid cell apoptosis

Relationships between the serum TPOAb and TGAb antibody distributions and water iodine concentrations, thyroid hormones and thyroid diseases: a cross-sectional study of 2503 adults in China

The aim of this study was to explore the status of thyroid peroxidase antibody (TPOAb) and thyroglobulin antibody (TGAb) in three areas with differing water iodine concentrations; and to discuss the relationships between these two thyroid antibodies and thyroid diseases in the three areas. We investigated 2503 adults from three areas. Urinary iodine concentrations, thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3), TPOAb, TGAb and thyroid volume (TV) were measured, and thyroid ultrasonography was performed. The positivity rates of TGAb(+), TPOAb(+) and TGAb(+) and TPOAb(+) or TGAb(+) were significantly higher in iodine fortification (IF) areas than iodine adequate (IA) areas (all P < 0·05). In IF and iodine excess areas, the positivity rates of TPOAb(+), TGAb(+) and TPOAb(+) or TGAb(+) significantly increased with age (all P for trend < 0·05). The levels of TSH, TV and the prevalence of overt hypothyroidism, subclinical hypothyroidism and goitre were significantly elevated in the thyroid antibody-positive groups in the three areas, but the FT3 was diminished (all P < 0·010). Positivity for TPOAb and TGAb was associated with an increased risk of subclinical hypothyroidism in the three areas. In areas with different median water iodine, positivity for both TPOAb and TGAb was associated with elevated TSH values. Notably, with the increased levels of TPOAb, the frequency of abnormally elevated TSH increased dramatically in the three areas.

Thyroid diseases and second to fourth digit ratio in Polish adults

The association between second to fourth finger ratio and thyroid diseases is unexplained. There is a possible interaction between prenatal exposition to sex hormone and thyroid functions in the adulthood. The study included 175 adults investigated in Łódź in the central Poland. It consisted of two main parts: a survey including questions about occurrence of thyroid gland dysfunction and anthropometric measurements (body mass and height and length of the second and fourth finger, waist and hip circumferences). The women who had thyroid disease had higher 2D:4D digit ratio (left hand) (mean = 1.004; SD = 0.036) than healthy ones (mean = 0.989; SD = 0.030) (t = − 2105; p = 0.038; d = 0.707). The association between thyroid diseases occurrence and prenatal steroid hormone exposition is noticed. Only females who had thyroid diseases tend to have higher 2D:4D digit ratio, for left hand.

Birth control pills and risk of hypothyroidism: a cross-sectional study of the National Health and Nutrition Examination Survey, 2007-2012

OBJECTIVE

The association between use of birth control pills and thyroid function in women has not ever been well studied, but potential risk has been implicated by small sample-sized studies. We aimed to determine this association using a large epidemiological survey.

DESIGN

Cross-sectional study.

SETTING

National Health and Nutrition Examination Survey conducted in the USA from 2007 to 2012.

PARTICIPANTS

Female respondents aged 18+ who had data on history of taking birth control pills and thyroid function were included. History of taking birth control pills was based on responses on the reproductive health questionnaire. Participants not on antithyroid medication with thyroid-stimulating hormone (TSH) >5.6 mIU/L and those on thyroid hormone replacement regardless of TSH were categorised as hypothyroid. Participants not on thyroid hormone replacement or antithyroid medication who had TSH between 0.34 mIU/L and 5.6 mIU/L were classified as euthyroid.

PRIMARY AND SECONDARY OUTCOME MEASURES

Association between use of birth control pills and hypothyroidism based on multivariate logistic regression analysis.

RESULTS

A total of 5116 female adults with history of taking birth control pills (n=3034) and without (n=2082) were included. A higher prevalence of hypothyroidism was found in those who have ever taken birth control pills (17.7% vs 14.1%; p=0.003). Multivariate logistic regression adjusted for confounding covariables, including age, race, education, body mass index, smoking status, alcohol use, history of thyroid disease, current thyroid disease, first menstrual age, pregnancy history, menopause status and history of hormone replacement use, demonstrated a significant association between history of taking birth control pills for more than 10 years and hypothyroidism (OR, 3.837; 95% CI 1.402 to 10.500; p=0.009).

CONCLUSIONS

Longer history of using birth control pills was strongly associated with hypothyroidism, especially for more than 10 years.

Parity and 11-Year Serum Thyrotropin and Thyroid Autoantibody Change: A Longitudinal Population-Based Study

BACKGROUND

A role for female reproductive factors in the pathogenesis of thyroid autoimmunity has been suggested. This study investigated the prospective association between parity, abortion, use of oral contraceptive pill (OCP), and use of hormone replacement therapy (HRT), and 11-year change in serum thyrotropin (TSH), as well as change in thyroid peroxidase autoantibody (TPOAb) status.

METHODS

A random sample of 4649 people aged 18-65 years participated in a population-based study in the period 1997-1998. In the study presented here, 1749 non-pregnant women with no history of thyroid disease were included who participated in the 11-year follow-up examination in the period 2008-2010. Gynecological exposures were reported in a self-administered questionnaire at baseline and follow-up. TSH and TPOAb were measured at baseline and follow-up. Increased TPOAb status during follow-up was defined as a TPOAb below the assay cutoff (<30 kIU/L) at baseline and a TPOAb ≥30 kIU/L at follow-up. Multiple linear regression models were used, adjusted for age, smoking status, and urinary iodine excretion.

RESULTS

An inverse association was found between the number of years on HRT and the risk (odds ratio) of increased TPOAb status during follow-up (0.735 [confidence interval 0.558-0.968], p = 0.03). However, this association was not statistically significant when applying the Bonferroni adjusted significance level. The remaining reproductive factors showed no statistically significant association with risk of increased TPOAb during follow-up. Furthermore, parity, abortions, use of OCP, HRT use, age at menarche, and being pre- or postmenopausal were not significantly associated with 11-year TSH change.

CONCLUSIONS

No statistically significant association was found between the studied female reproductive measures and 11-year risk of TSH or TPO change. A possible protective role for HRT in the etiology of thyroid autoimmunity, however, deserves further research.

Two faces of the estrogen metabolite 2-methoxyestradiol in vitro and in vivo

2-Methoxyestradiol (2-ME), an endogenous metabolite of 17β-estradiol (E2), interacts with estrogen receptors (ERs) and microtubules, however, 2-ME has a low affinity for ERs. Furthermore, 2‑ME has been identified as a potential novel antitumor agent, combining its anti‑proliferative effects on a variety of tumor cell types with its anti‑angiogenic action. Therefore, 2‑ME is of interest due to its potential anticancer therapeutic effects. In the current study, the estrogenic effect of 2‑ME on CaBP‑9k, ERα, and progesterone receptor (PR) mRNA levels in the absence and presence of E2 and progesterone (P4) in in vivo and in vitro models was examined. In GH3 cells, the mRNA level of CaBP‑9k was induced in the E2 treatment group (concentration, 10‑9 M), and the expression of CaBP‑9k was also upregulated in the 2‑ME‑treated group (concentration, 10‑7 M). Uterine lactoferrin (Ltf) mRNA expression was also increased in the 2‑ME group [dose, 40 mg/kg body weight (BW)], which was comparable to the response with E2 (dose, 40 µg/kg BW) observed in mice. As inhibitors of ER and PR activity, ICI 182,780 and mifepristone (RU486) were observed to reverse the E2 or 2‑ME mediated increase of CaBP‑9k and Ltf mRNA expression. In addition, it was found that 2‑ME significantly decreased the levels of ERα and increased PR transcripts. Consistent with the in vitro results, the mRNA levels revealed decreased ERα and increased PR in in vivo treatment of E2 and 2‑ME. These findings demonstrate that the expression of estrogenic markers, CaBP‑9k and Ltf, is regulated by 2‑ME in in vitro and in vivo models, therefore, estrogenic activi-ties of 2-ME may be increased in females during the estrous cycle via the ER and/or PR-mediated signaling pathway.

Genetic and non-iodine-related factors in the aetiology of nodular goitre

Genetic and a large number of environmental non-iodine-related factors play a role in the cause of nodular goitre. Most evidence for the influence of genetic and environmental factors in the cause of goitre is from cross-sectional, population-based studies. Only a few studies have included prospective data on risk factors for nodular goitre, although few prospective data are available on the effect of iodine and tobacco smoking on goitre development. Goitre is not one single phenotype. Many epidemiological studies do not distinguish diffuse from nodular goitre, as the investigated parameter is often thyroid volume or frequency with increased thyroid volume. Moreover, information on the presence and effect of gene-environment, gene-gene, and environment-environment effect modifications is limited. Thus, firm conclusions about the relative contributions and causality of the investigated risk factors should be made with caution. Smoking seems to be an established risk factor for nodular goitre, possibly with effect modification from iodine intake, as the risk associated with smoking is smaller or absent in areas with sufficient iodine intake. The use of oral contraceptives might have protective effects against goitre, and childbirth is an increased risk factor for goitre in areas with non-optimal iodine intake. Insulin resistance is a recently investigated risk factor, and the risk of goitre may be reversible with metformin treatment. Iodine remains the major environmental risk factor for nodular goitre.

Impact of body mass index on thyroid functions in Indian children

OBJECTIVE

There is controversy about the relation of thyroid functions and body mass index. The present study was aimed to assess the relationship between thyroid function and body mass index in Indian school children.

DESIGN

Population survey.

PATIENTS

Data were collected from 25 schools in 19 cities across five different geographical zones of India. Children, who consented, were evaluated for anthropometry and blood tests. Children were categorized as overweight and obese based on standard BMI criteria.

MEASUREMENTS

Serum samples were analysed for free T3, free T4, TSH and anti-TPO antibodies.

RESULTS

A total of 13,691 children in the age group of 5-18 years formed the study population. The mean age and mean BMI were 11·9 ± 3·0 years and 18·48 ± 3·89 kg/m² respectively. Among these, 2119 (15·5%) children were overweight and 536 (3·9%) were obese. Subclinical hypothyroidism was present in 943 (6·9%) children.FT3 and TSH levels increased and FT4 levels decreased with increasing BMI in euthyroid boys and girls. Prevalence of SCH was significantly higher in obese/overweight children (9·0%, vs 6·5%; P = 0·034) as compared with normal BMI children.

CONCLUSIONS

Serum FT3 and TSH were positively while FT4 was negatively associated with BMI in apparently healthy euthyroid children.

Overweight increases risk of first trimester hypothyroxinaemia in iodine-deficient pregnant women

Hypothyroxinaemia early in pregnancy may impair fetal brain development. Increased body weight has been associated with low thyroxine concentrations in non-pregnant women. In pregnant women, morbid maternal obesity is a risk factor for thyroid dysfunction. But whether lesser degrees of overweight that are much more common could be a risk factor for hypothyroxinaemia in pregnancy is unclear. The objective of this study was to investigate if overweight increases risk for thyroid dysfunction, and specifically hypothyroxinaemia, in iodine-deficient pregnant women. We performed a cross-sectional study at first hospital visit among healthy Thai pregnant women. We measured weight and height, urinary iodine concentration (UIC), serum thyroid hormones and thyroglobulin. Pre-pregnancy weight and relevant dietary factors were determined by questionnaire, and body mass index (BMI) was used to classify weight status. Among 514 women (mean gestational age, 11 weeks) with a median UIC of 111 μg dL(-1) , indicating mild iodine deficiency, 12% had low free thyroxine (fT4) concentrations: 3% had overt hypothyroidism; 7% had subclinical hypothyroidism; and 8% had isolated hypothyroxinaemia. Based on pre-pregnancy BMI, 26% of women were overweight or obese. In a multiple regression model, BMI was a negative predictor of fT4 (β = -0.20, P < 0.001). Compared to normal weight women, the prevalence ratio (95% CI) of a low fT4 in overweight women was 3.64 (2.08-6.37) (P < 0.01). Iodine-deficient pregnant Thai women who are overweight have a 3.6-fold higher risk of hypothyroxinaemia in the first trimester compared to normal weight women. Targeted screening should consider overweight a potential risk factor for thyroid dysfunction in pregnant women in iodine-deficient areas.

2D/3D-QSAR STUDY ON ANALOGUES OF 2-METHOXYESTRADIOL WITH ANTICANCER ACTIVITY

Two-dimensional (2D) and three-dimensional (3D) quantitative structure–activity relationships (QSARs) of 23 analogs of 2-Methoxyestradiol with anticancer activity (expressed as p GI50) against MCF-7 human breast cancer cells have been studied by using a combined method of the DFT, MM2 and statistics for 2D, as well as the comparative molecular field analysis (CoMFA) for 3D. The established 2D-QSAR model in training set shows not only significant statistical quality, but also predictive ability, with the square of adjusted correlation coefficient [Formula: see text] and the square of the cross-validation coefficient (q2= 0.779). The same model was further applied to predict p GI50values of the four compounds in the test set, and the resulting [Formula: see text] being as high as 0.827, further confirms that this 2D-QSAR model has high predictive ability for this kind of compound. The 3D-QSAR model also shows good correlative and predictive capabilities in terms of R2(0.927) and q2(0.786) obtained from CoMFA model. The results that 2D- and 3D-QSAR analyses accord with each other, suggest that the electrostatic interaction plays a decisive role in determining the anticancer activity of the studied compounds, and that increasing the negative charge of substituent R2and the positive charge of substituents linking to C17as well as decreasing the size of substituent R1are advantageous to improving the cytotoxicity. Such results can offer some useful theoretical references for directing the molecular design and understanding the action mechanism of this kind of compound with anticancer activity.

Influence of dendrimer surface charge on the bioactivity of 2-methoxyestradiol complexed with dendrimers

We report the complexation of a potential anticancer agent 2-methoxyestradiol (2-ME) with generation 5 (G5) poly(amidoamine) dendrimers having different surface functional groups for therapeutic applications. The complexation experiment shows that approximately 6-8 drug molecules can be complexed with one dendrimer molecule regardless the type of the dendrimer terminal groups. The bioactivity of 2-ME complexed with dendrimers was found to be significantly dependent on the surface charge of G5 dendrimers. In vitro cell biological assays show that amine, hydroxyl, and acetamide-terminated G5 dendrimers with positive, slightly positive, and close to neutral surface charges, respectively are able to deliver 2-ME to inhibit cancer cell growth. In contrast, 2-ME complexed with carboxyl-terminated G5 dendrimers with negative surface charges does not show its inherent bioactivity. Further molecular dynamics simulation studies show that the compact structure of carboxylated G5 dendrimers complexed with 2-ME does not allow the release of the drug molecules even at a pH of 5.0, which is the typical pH value in lysosome. Our findings indicate that the surface modification of dendrimers with different charges is crucial for the development of formulations of various anticancer drugs for therapeutic applications.

In vitro effects of 2-methoxyestradiol on cell numbers, morphology, cell cycle progression, and apoptosis induction in oesophageal carcinoma cells

The influence of 2-methoxyestradiol (2-ME) was investigated on cell numbers, morphology, cell cycle progression, and apoptosis induction in an oesophageal carcinoma cell line (WHCO3). Dose-dependent studies (1 x 10(-9)M-1 x 10(-6)M) revealed that 2-ME significantly reduced cell numbers to 60% in WHCO3 after 72 h of exposure at a concentration of 1 x 10(-6)M compared to vehicle-treated cells. Morphological studies entailing light-, fluorescent-, as well as transmission electron microscopy (TEM) confirmed 2-ME's antimitotic effects. These results indicated hallmarks of apoptosis including cell shrinkage, hypercondensation of chromatin, cell membrane blebbing, and apoptotic bodies in treated cells. Flow cytometric analyses demonstrated an increase in the G(2)/M-phase after 2-ME exposure; thus preventing cells from proceeding through the cell cycle. beta-tubulin immunofluorescence revealed that 2-ME caused spindle disruption. In addition, increased expression of death receptor 5 protein was observed further supporting the proposed mechanism of apoptosis induction via the extrinsic pathway in 2-ME-exposed oesophageal carcinoma cells.

Therapeutic efficacy of 2-methoxyestradiol microcrystals encapsulated within polyelectrolyte multilayers

Development of a novel formulation of anticancer drugs to improve their water-solubility and bioavailability remains a great challenge. Herein, the potential anticancer agent 2-methoxyestradiol (2-ME) was selected as a model drug and was encapsulated within polyelectrolyte (PE) multilayers by layer-by-layer deposition of oppositely charged PEs onto the drug microcrystal surfaces. Cell viability and morphology observation of two cell lines reveal that the PE multilayer-encapsulated 2-ME microcrystals markedly decrease the cell viability, displaying similar inhibitory effect to that of the conventional formulation of 2-ME dissolved in ethanol. The current approach to encapsulate hydrophobic drug microparticles may be useful for formulating different drugs for a variety of biological applications.

The role of steroid hormones in the NF1 phenotype: focus on pregnancy

The Neurofibromatosis Type 1 (NF1) gene functions as a tumor suppressor gene. Loss of its protein, neurofibromin, in the autosomal dominant disorder NF1 is associated with peripheral nervous system tumors, particularly neurofibromas, benign lesions in which the major cell type is the Schwann Cell (SC). Benign and malignant human tumors found in NF1 patients are heterogeneous with respect to their cellular composition. The number and size of neurofibromas in NF1 patients has been shown to increase during pregnancy, with, in some cases, post-partum regression, which suggests hormonal involvement in this increase. However, in this review, we consider evidence from the literature that both direct hormonal influence on tumor growth and on angiogenesis may contribute to these effects.

Influence of hormones and hormone metabolites on the growth of Schwann cells derived from embryonic stem cells and on tumor cell lines expressing variable levels of neurofibromin

Loss of neurofibromin, the protein product of the tumor suppressor gene neurofibromatosis type 1 (NF1), is associated with neurofibromas, composed largely of Schwann cells. The number and size of neurofibromas in NF1 patients have been shown to increase during pregnancy. A mouse embryonic stem cell (mESC) model was used, in which mESCs with varying levels of neurofibromin were differentiated into Schwann-like cells. NF1 cell lines derived from a malignant and a benign human tumor were used to study proliferation in response to hormones. Estrogen and androgen receptors were not expressed or expressed at very low levels in the NF1+/+ cells, at low levels in NF1+/-cells, and robust levels in NF1-/-cells. A 17beta-estradiol (E2) metabolite, 2-methoxy estradiol (2ME2) is cytotoxic to the NF1-/- malignant tumor cell line, and inhibits proliferation in the other cell lines. 2ME2 or its derivatives could provide new treatment avenues for NF1 hormone-sensitive tumors at times of greatest hormonal influence.

The complex role of estrogens in inflammation

There is still an unresolved paradox with respect to the immunomodulating role of estrogens. On one side, we recognize inhibition of bone resorption and suppression of inflammation in several animal models of chronic inflammatory diseases. On the other hand, we realize the immunosupportive role of estrogens in trauma/sepsis and the proinflammatory effects in some chronic autoimmune diseases in humans. This review examines possible causes for this paradox. This review delineates how the effects of estrogens are dependent on criteria such as: 1) the immune stimulus (foreign antigens or autoantigens) and subsequent antigen-specific immune responses (e.g., T cell inhibited by estrogens vs. activation of B cell); 2) the cell types involved during different phases of the disease; 3) the target organ with its specific microenvironment; 4) timing of 17beta-estradiol administration in relation to the disease course (and the reproductive status of a woman); 5) the concentration of estrogens; 6) the variability in expression of estrogen receptor alpha and beta depending on the microenvironment and the cell type; and 7) intracellular metabolism of estrogens leading to important biologically active metabolites with quite different anti- and proinflammatory function. Also mentioned are systemic supersystems such as the hypothalamic-pituitary-adrenal axis, the sensory nervous system, and the sympathetic nervous system and how they are influenced by estrogens. This review reinforces the concept that estrogens have antiinflammatory but also proinflammatory roles depending on above-mentioned criteria. It also explains that a uniform concept as to the action of estrogens cannot be found for all inflammatory diseases due to the enormous variable responses of immune and repair systems.

SAR studies of 2-methoxyestradiol and development of its analogs as probes of anti-tumor mechanisms

The major estrogen metabolite 2-methoxyestradiol (2ME) has been shown to target tumor cells without severe side effects and is currently being evaluated in clinical trials for several types of cancer. Despite its promise for use in clinical setting, the mechanism(s) by which 2ME exerts its anti-tumor activity is not clearly defined at this time. Employing organic chemistry tools, we synthesized 2ME analogs with which 2ME affinity column was prepared, enabling us to detect a protein that selectively interacts with 2ME. This 2ME analog will be useful as a probe to identify the biological target(s) of 2ME and study their functions in tumor cells.

2-methoxyestradiol induces apoptosis in cultured human anaplastic thyroid carcinoma cells

Anaplastic thyroid carcinoma (ATC) is one of the most malignant tumors in humans, and currently there is no effective treatment. In the present study we investigated the effect of an endogenous estrogen metabolite, 2-methoxyestradiol (2-ME), on the growth of human ATC cells. 2-ME treatment had a strong growth inhibitory effect on five human ATC cell lines (HTh7, HTh 74, HTh83, C643, and SW1736), but showed no effect on one cell line (KAT-4). Cell cycle analysis of the growth-inhibited cells showed that 2-ME induced a G2/M-arrest, followed by an increased fraction of cells in sub-G1. Analysis of internucleosomal DNA laddering as well as DNA fragmentation in a terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) assay demonstrated a high number of cells undergoing apoptosis after 2-ME treatment. An increased activation of caspase-3 and caspase-8 by 2-ME was observed, and inhibition of caspase-3 decreased the apoptotic effect. Addition of 2-ME increased activity of p38 mitogen-activated protein kinase (MAPK) in the sensitive HTh7 as well as the refractory KAT-4 cells, however, activation of stress-activated protein kinase/c-jun aminoterminal kinase (SAPK/JNK) was seen only in the HTh7 cells. Inhibitors of p38 MAPK and SAPK/JNK significantly attenuated the 2-ME effect. Taken together, our data demonstrate an antiproliferative and apoptotic effect of 2-ME on ATC cells involving activation of MAPKs.

Genotoxicity of hormonal steroids

Hormonal steroids have a widespread use in medicine and their side effects are continuously debated. The possible genotoxic activity of steroids has been the subject of many investigations. The natural estrogens estradiol, estrone and estriol are generally negative in the ICH core battery of tests, but several positive results have been obtained when using additional endpoints of genotoxicity. The genotoxic activity of the 4-hydroxy metabolites of estradiol and estrone is well established. The synthetic steroidal estrogens have a comparable profile of negative and positive test results. Cyproterone acetate and some of its analogues have a special position within the group of progestins. Their genotoxic potential has been established. Other progestins are generally negative in the routine tests. Anti-glucocorticoids, anti-progestins, corticosteroids, androgens, anabolics and anti-androgens appear to be devoid of genotoxic activities. The genotoxic potential of estradiol, estrone and cyproterone acetate with its analogues may play no role under normal physiological and therapeutic conditions. The metabolic conditions that are needed for the formation of DNA-reactive metabolites and oxygen radicals may not be present in humans. Epidemiological cancer data seem to support this view. The importance of thresholds in the dose-effect-relationship of genotoxicity data and their use in risk assessment is discussed.

Free radical stress in chronic lymphocytic leukemia cells and its role in cellular sensitivity to ROS-generating anticancer agents

2-Methoxyestradiol (2-ME), a new anticancer agent currently in clinical trials, has been demonstrated to inhibit superoxide dismutase (SOD) and to induce apoptosis in leukemia cells through a free radical-mediated mechanism. Because the accumulation of superoxide (O(2)-) by inhibition of SOD depends on the cellular generation of O(2)-, we hypothesized that the endogenous production of superoxide may be a critical factor that affects the antileukemia activity of 2-ME. In the present study, we investigated the relationship between cellular O(2)- contents and the cytotoxic activity of 2-ME in primary leukemia cells from 50 patients with chronic lymphocytic leukemia (CLL). Quantitation of O(2)- revealed that the basal cellular O(2)- contents are heterogeneous among patients with CLL. The O(2)- levels were significantly higher in CLL cells from patients with prior chemotherapy. CLL cells with higher basal O(2)- contents were more sensitive to 2-ME in vitro than those with lower O(2)- contents. There was a significant correlation between the 2-ME-induced O(2)- increase and the loss of cell viability. Importantly, addition of arsenic trioxide, a compound capable of causing reactive oxygen species (ROS) generation, significantly enhanced the activity of 2-ME, even in the CLL cells that were resistant to 2-ME alone. These results suggest that the cellular generation of O(2)- plays an important role in the cytotoxic action of 2-ME and that it is possible to use exogenous ROS-producing agents such as arsenic trioxide in combination with 2-ME to enhance the antileukemia activity and to overcome drug resistance. Such a combination strategy may have potential clinical applications.

Dose-response effects of 2-methoxyestradiol on estrogen target tissues in the ovariectomized rat

In three experiments, we evaluated the pharmacological effects of 2-methoxyestradiol (2ME(2)) on several estrogen target tissues. Experiment 1: we gavaged recently ovariectomized (OVX) 9.5-wk-old rats with 2ME(2) at doses of 0, 0.1, 1, 4, 20, and 75 mg/kg in a 21-d dose-response study. 2ME(2) reduced body weight and serum cholesterol, increased uterine weight and epithelial cell height, and inhibited longitudinal and radial bone growth compared with values in the untreated OVX rat. All doses of 2ME(2) maintained cancellous bone mass at the baseline level, the lowest effective dose being 20-fold less than a uterotrophic dose. Experiment 2: in an 8-wk experiment in adult OVX rats, a nonuterotrophic dose of 2ME(2) (4 mg/kg x d) suppressed body weight gain, inhibited bone formation in cancellous bone and partially prevented bone loss in the tibial metaphysis. Experiment 3: in weanling rats, ICI 182,780 did not antagonize the effect of 2ME(2). We conclude that 2ME(2) antagonizes the skeletal changes that follow OVX at doses that have minimal or no effects in the uterus in both young and adult rats; 2ME(2) does not appear to act via estrogen receptors and is active on bone at doses well below those required for tumor suppression in mice. 2ME(2), through a novel pathway, may be a useful alternative to conventional hormone replacement therapy for prevention of postmenopausal bone loss.

Prolonged effects of beta-estradiol 3-benzoate on thyroid tumorigenesis in gonadectomized rats pretreated with N-bis(2-hydroxypropyl)nitrosamine

The prolonged modulatory effects of beta-estradiol 3-benzoate (EB), a synthetic estrogenic compound, were investigated in a rat two-stage thyroid tumorigenesis model. One week after a single subcutaneous (s.c.) injection of N-bis(2-hydroxypropyl)nitrosamine, gonadectomized F344 rats of both sexes were s.c. implanted with fused pellets containing EB for 32 weeks. Doses of EB at 0, 0.004, 0.02 and 0.1mg were achieved by varying the ratio of EB to cholesterol in the pellet. Major organs including the thyroid, pituitary, liver, kidneys, uterus and brain were weighed and histopathological observation was performed. Serum was assayed for triiodothyronine (T(3)), thyroxine (T(4)) and thyroid-stimulating hormone (TSH). Thyroid weights were increased by the EB pellet implantation in a dose-dependent manner and significantly (P<0.05) elevated in the 0.1mg EB male group and in the 0.02 and 0.1mg EB female groups. The EB treatments dose-dependently suppressed serum T(4) levels and inversely elevated serum TSH levels in both sexes but without statistical significance in females. Histopathologically, EB increased the occurrence of thyroid proliferative lesions in males and showed a tendency for increase in females. Interestingly, the effect of EB was more intensive in males than in females, even the lowest dose inducing a follicular carcinoma in a male. These results, thus indicate the possible contribution of prolonged EB stimulation at lower doses to thyroid tumorigenesis without additional promotive condition.

Testosterone and estradiol up-regulate androgen and estrogen receptors in immature and adult rat thyroid glands in vivo

Thyroid gland is one of the non-classical target organs for sex steroids. Presence of androgen and estrogen receptors in the neoplastic and non-neoplastic thyroid glands of mammalian species is well documented. The aim of the present study is to elucidate the changes in serum and thyroidal sex steroids, and their receptors in the thyroid gland of rats from immature to adult age under gonadectomized (GDX) and sex steroids replaced conditions. Normal Wistar male and female rats from immature to adult age (day 21, 30, 45, 60 and 160 post-partum (pp)) were used in the present study. One group (I) of rats was GDX at an early age (day 10 pp) and the other group (II) at the adult age (day 120 pp). Group I rats were sacrificed at different experimental periods such as 21, 30, 45 and 60 days pp, and group II rats were sacrificed at day 160 pp. Another group of GDX rats from group I and II were replaced with physiological doses of testosterone or estradiol. Serum and thyroidal concentrations of sex steroids were estimated by RIA method and the concentrations of receptors by radioreceptor assay. Gonadectomy significantly decreased serum and thyroidal testosterone and estradiol and concentrations of androgen receptor (AR) and estrogen receptor (ER) in the thyroid. Replacement of sex steroids to GDX rats restored the normal level of sex steroids, AR and ER. Therefore, it is suggested from the present study that (i). sex steroids up-regulate their own receptors in the thyroid, (ii). sex steroids may influence thyroid growth and the proliferation of thyrocytes by modulating their receptor concentrations in the thyroid.

Risk factors for goiter and thyroid nodules

The occurrence of thyroid diseases is determined by interplay between genetic and environmental factors. The major environmental factor that determines goiter prevalence is iodine status, but other environmental factors influencing entire populations have been identified such as goitrogens in food and drinking water. Less focus has been on individual environmental factors and the interplay between factors. The goiter prevalence is higher in certain groups in the population. The variation in goiter prevalence between the genders is well known with a higher occurrence among women. The association with age is probably dependent on iodine status, because it seems that the zenith of goiter prevalence appears earlier in life the more severe iodine deficiency the population is exposed to. The association with individual risk factors has been investigated in some studies, especially the association with tobacco smoking. In iodine-deficient areas, a strong association between tobacco smoking and goiter prevalence is found, whereas the association is less pronounced in iodine-replete areas. This was predictable from experimental studies showing thiocyanate to be the mediator of the goitrogenic effect of tobacco smoke acting as a competitive inhibitor of iodine uptake. The association with alcohol intake has only been investigated in few studies, but a low occurrence of goiter among alcohol consumers has been found. The mechanism of this association is not known. Increased goiter prevalence during pregnancy has been reported, and recently a long-term goitrogenic effect of pregnancies has also been shown. As demonstrated for tobacco smoking, this association is dependent on iodine status, because the association has only been found in areas with a suboptimal iodine intake. This indicates pregnancy-induced goiter to be the result of exacerbation of existing iodine deficiency. Recently, the use of oral contraceptives has been shown to be associated with a markedly reduced prevalence of goiter, although experimental studies have previously shown proliferative effects of estrogens on thyrocytes. Some implications for prevention of thyroid disease could be suggested. Discussion of smoking habits should be included in a consultation for goiter with a motivation to quit smoking. Iodine deficiency has particularly strong goitrogenic effects during pregnancy and for the sake of the mother as well as the fetus, sufficient iodine supply should be ensured to all pregnant women. The difference in age maximum in goiter prevalence suggests that monitoring of iodine deficiency disorders should ideally include a spectrum of age groups.

Low goitre prevalence among users of oral contraceptives in a population sample of 3712 women

OBJECTIVE

Goitre occurs primarily in women. As oestrogens may be an aetiologic factor, the use of oral contraceptives (OC) could be associated with an increased risk of goitre. This is supported by experimental data, but a recent population study suggested decreased thyroid volumes among users of OC.

DESIGN

Cross-sectional, observational study.

PARTICIPANTS

A random population sample of 3712 women from two Danish cities.

MEASUREMENTS

Ultrasound and clinical examination of the thyroid, measurement of serum TSH, T3, T4 and thyroglobulin, and personal interviews with registration of use of OC or post-menopausal oestrogen therapy. Data were analysed in linear models and logistic regression adjusting for age and iodine status.

RESULTS

Thyroid volume was lower among users than non-users of OC, 11.1 ml vs. 12.1 ml (P < 0.001). Use of OC was correspondingly associated with a reduced prevalence of thyroid enlargement on ultrasound (odds ratio 0.53, 95% confidence interval 0.37-0.74) and of palpable and visible goitre (OR 0.24, 95% CI 0.07-0.81). Serum TSH was 1.24 mU/l in non-users of OC and 1.35 mU/l in users (P = 0.002). The percentage of goitre cases prevented by OC compared to a hypothetical population without use of OC was 29%. Post-menopausal oestrogen therapy showed similar, but statistically non-significant, associations.

CONCLUSION

Use of oral contraceptives was associated with a lower thyroid volume and reduced risk of goitre, and clinically evident goitre was four times more frequent among non-users than among users of oral contraceptives.