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Soy extracts suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes
Abstract
Soy consumption is associated with thyroid disorders such as hypothyroidism, goiter, and autoimmune thyroid disease (ATD) as well as increased iodine requirement in certain cases. However, the anti-thyroid component(s) in soy are yet to be identified and the molecular mechanism(s) involved remain unclear. This study examined the effects of soy isoflavones (ISF) on iodide uptake and expression of thyroglobulin (Tg) and sodium/iodide symporter (NIS) in thyrocytes. Fischer rat thyroid cells (FRTL) were treated with Novasoy (a soy alcohol extract containing 30% ISF) or major ISF aglycones or glycosides for 24 h. Iodide uptake was measured by a colorimetric assay. The protein level of Tg and NIS was measured by Western blotting. Cytotoxicity of tested compounds was determined by the MTT cell proliferation assay. Iodide uptake in FRTL cells was dose-dependently suppressed by Novasoy added into the cell culture (10, 25, or 50 µg/mL, P < 0.05). However, neither the major ISF aglycones nor glycosides alone or in combination had similar effects. Novasoy (up to 200 µg/mL) had no cytotoxic effect. Novasoy (1, 10, and 50 µg/mL) and genistein (1 and 10 µM) markedly increased the protein content of a 40 kDa Tg fragment (P40, a known autoimmunogen) and non-glycosylated NIS in the FRTL cells (P < 0.05). Overall, this study demonstrated that the alcohol soluble component(s) other than the major ISF in soy remarkably inhibited iodide uptake in the FRTL cells. Soy ISF, particularly genistein, induced the production of P40, which might be responsible for the higher incidence of ATD reported in soy infant formula-fed children.
... A low iodine diet (LID) has been suggested 2 weeks prior to radioiodine administration for patients with differentiated thyroid carcinoma after thyroidectomy to enhance radioiodine uptake in remnants or residual tumor to ensure effective ablation or treatment (1,2). Available data indicate that the alcohol soluble component in soybeans inhibits thyroid absorption of iodine and thus interferes with radioiodine thyroid uptake, leading to reduced efficacy of radioiodine therapy (3). Soy sauces are made from soybeans and are not recommended during a LID (2,(4)(5)(6). ...
... Soy sauces are made from soybeans and are not recommended during a LID (2,(4)(5)(6). Soybeans per se do not contain iodine, but soy sauces may contain iodine if iodized salts are added during the fermentation process or if food additives such as seaweeds or yeasts are added during processing to enhance the flavor of soy sauces (3,7). ...
Background
Soy sauce is widely used in a variety of Asian dishes to enhance flavor. Soybean and most soybean products, including soy sauces, are listed as prohibited foods in a low iodine diet. However, the iodine content in soy sauces is largely unknown. The aim of this study was to determine the iodine content in domestic soy sauces in Taiwan.
Methods
Twenty-five different kinds of soy sauces were diluted with distilled water and with a dilution factor of fifty or above. Iodine concentrations of the diluted samples were measured colourimetrically based on the Sandell-Kolthoff reaction by a modified microplate method. All the measurements were repeated twelve times on three different days for determination of mean and standard deviation (SD), and coefficients of variance (CV). Serial dilution and recovery tests were also performed for validation. The results were confirmed by an inductively coupled plasma mass spectrometry (ICP-MS) method.
Results
Among the twenty-five surveyed soy sauces, most of them (n=22) were iodine-free (<16 ug/L, and thus un-detectable). The iodine concentrations (mean ± SD) of the three iodine-containing soy sauces were 2.7 ± 0.1, 5.1 ± 0.2, and 10.8 ± 0.6 mg/L, respectively. The inter-assay, intra-assay and total CVs were all <5.3% for the modified microplate method. The results obtained by ICP-MS were consistent with those of the modified microplate method. The recovery rates in the serial dilution test and recovery test ranged from 94.7% to 118.6%. Two of the three iodine-containing soy sauces were supplemented with kelp extract, while the other one without kelp extract had the highest amount of salt among the three iodine-containing soy sauces. Therefore, we postulate that iodized salt instead of kelp extract is the source of higher iodine content in that sauce.
Conclusion
The results suggest that most soy sauces are iodine-free and may be allowed during low iodine diets.
... Several research reports have confirmed an association between excessive intake of soybeans and hypothyroidism ( [14], [15], [16], [17]). Based on this correlation, this study aimed to study the possibility of controlling excessive thyroid hormonal secretions by extracting the water soybean seed. ...
... Also re. [17] refer to the effect of esoflavones soybean which inhibition iodine taken. Re. [24] refers to that adding soybean to the daily food of male mice by 50 % for 9 weeks causing reduction in teroxine levels. ...
... Limiting the consumption of these foods (twice a month or less) is recommended, despite the potential human health benefits of soy in the prevention of cancer, cardiovascular diseases, the reduction of menopause symptoms, increased bone-mineral density, and decreased insulin resistance [83]. Conversely, soy has raised concern about thyroid gland function [84]. According to Messina et al., the literature provides little evidence that the consumption of soy foods or isoflavones has adverse effects for euthyroid individuals with iodine deficiency. ...
... Thus, it is vital that consumers of soy-based foods be sure that their iodine intake is adequate. In addition, soy may hinder the absorption of thyroid drugs [84]. ...
The current state of knowledge related to diet in Hashimoto thyroiditis (HT) is far from satisfactory, as many HT subjects experience several disorders and report reduced quality of life. There are three aims of the study: (1) to develop a qualitative dietary protocol (QDP; ‘Diet4Hashi’) as a simple, graphic–text tool dedicated to TH subjects, (2) to evaluate the use of the QDP in dietetic counseling compared to conventional dietetic counseling (CDC) in HT women, and (3) to assess the impact of both the QDP and the CDC on the diet quality, quality of life, adiposity, and metabolic parameters of HT women. The QDP is based on subject self-monitoring supported with a graphic–text tool to help them in food selection and adequate food frequency consumption, while the CDC on oral explanation and printed sample menus were provided by a dietician. The QDP contains two lists: (A) foods recommended for consumption and (B) foods with limited consumption, along with indicated consumption frequency per day/week/month. Both approaches include the same dietary recommendations for HT extracted from the literature but differ in subject–dietician cooperation. To summarize the evidence regarding dietary recommendations in HT, the PubMed, Embase, and Cochrane Library databases (to March 2019) and the bibliographies of key articles were searched. The study is designed as a dietary intervention lasting six months in two parallel groups: experimental and control. In the experimental group, the QDP will be applied, while in the control group, the CDC will be applied. In total, the study will include a baseline of 100 women with diagnosed HT. The subjects will be randomly allocated into the experimental/control groups (50/50). Data related to diet quality and other lifestyle factors, nutrition knowledge, quality of life, thyroid function, body composition, blood pressure, serum fasting glucose, and lipid profile at baseline and after a six-month follow-up will be collected. This study was conducted to develop a dietary protocol (Diet4Hashi) that is easy to follow for HT subjects, and it will contribute to providing valuable data that are useful to dieticians and physicians. It is anticipated that this graphic–text qualitative dietary protocol, by improving food selection and diet quality, may reduce adiposity and improve metabolic parameters and the quality of life of HT women.
... 47 Although soy derivatives have shown great benefits in many aspects regarding the cardiovascular system and treating cancer in addition to managing menopausal irregularities, evidence shows that they have harmful effects on the thyroid gland. 48 Sathyapalan et al concluded that patients with subclinical hypothyroidism and are being on daily soy supplementation products can easily develop hypothyroidism. 49 In the same context, Mittal et al reported that in their population of women that were treated with a daily intake of 75 mg of isoflavones, they found that the level of T3 was significantly reduced in these women. ...
Many forms of thyroid diseases have been classified under autoimmune thyroid disease. These include hyperthyroidism or commonly known as Grave’s disease, and hypothyroidism commonly identified as Hashimoto’s thyroiditis. Many nutritional elements have been linked to the function of the thyroid gland as any disturbance in these elements can lead to the development of relevant thyroid diseases. The most important elements include iodine, iron, selenium, zinc, and soy. In this current manuscript, we aimed to discuss the effect of these nutritional elements on the development of thyroid diseases by reviewing relevant studies in the literature. Although it is widely known that iodine is an essential component for the synthesis and release of these hormones, exaggerated intake of iodine can also lead to the development of hypothyroidism by negative feedback mechanisms. Besides, it can also trigger abnormal autoimmune reactions which can lead to the development of AITD. Selenium is another important factor and evidence shows that it has been associated with Grave’s thyroiditis, however, further evidence is needed as recommended by previous investigations. Clinicians should also take care of iron, zinc, and soy levels during management to obtain a better prognosis.
... Soy extracts suppressed iodine uptake and increased the protein content of a known autoimmunogenic Tg fragment in Fischer rat thyroid cells (FRTL). These effects might be responsible for the association between higher incidence of Soy consumption with thyroid disorders such as hypothyroidism, goiter, and autoimmune thyroid disease [32]. ...
Nutraceuticals are defined as a food, or parts of a food, that provide medical or health benefits, including the prevention of different pathological conditions, and thyroid diseases, or the treatment of them. Nutraceuticals have a place in complementary medicines, being positioned in an area among food, food supplements, and pharmaceuticals. The market of certain nutraceuticals such as thyroid supplements has been growing in the last years. In addition, iodine is a fundamental micronutrient for thyroid function, but also other dietary components can have a key role in clinical thyroidology. Here, we have summarized the in vitro, and in vivo animal studies present in literature, focusing on the commonest nutraceuticals generally encountered in the clinical practice (such as carnitine, flavonoids, melatonin, omega-3, resveratrol, selenium, vitamins, zinc, and inositol), highlighting conflicting results. These experimental studies are expected to improve clinicians’ knowledge about the main supplements being used, in order to clarify the potential risks or side effects and support patients in their use.
... They found out that the frequency of feedings with soy-based milk formulas in early life was significantly higher in children with autoimmune thyroid diseases (prevalence 31%) as compared with their siblings (prevalence 12% p < 0.01) and healthy nonrelated control children (prevalence 13%, p < 0.02). More recently working in rodent, Tran and co-workers [298] showed that GEN, DAID, or glycitein and a soy extract suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes in vitro. However, cells were from rat, and the efficient doses were higher than 1 μM. ...
... Additionally, Novasoy, and in particular genistein, increased both Tg fragment (P40, an autoimmunogen) and nonglycosylated NIS protein levels in the FRTL cells. 44 An in vivo study evaluated the effects of stigmasterol, isolated from the bark of Butea monosperma on THs and glucose regulation in mice (2.6 mg/kg/day for 20 days). Stigmasterol was found to reduce serum T3 and T4 levels, and to cause a reduction of glucose levels and hepatic G-6-Pase activity. ...
About 1 of 10 women, particularly those older than 60 years of age, shows some degree of thyroid hormone deficiency. Thyroid diseases are generally characterized by perturbations of thyroid signaling homeostasis. The most common examples of thyroid diseases include hypothyroidism, hyperthyroidism, and several types of thyroid cancers. Phytochemicals have been shown to have either beneficial or detrimental effects on thyroid function. Some flavonoids have been reported to affect the expression and the activity of several thyroid‐related enzymes and proteins, and for this reason some concerns have been raised about the possible thyroid‐disruptive properties of foods enriched in these substances. On the other hand, the beneficial effects of some plant‐derived compounds, such as myricetin, quercetin, apigenin, rutin, genistein, and curcumin, and their possible role as adjuvants for the treatment of thyroid cancers have been described. Here, the role of phytochemicals in thyroid signaling modulation and their possible beneficial or detrimental effects on thyroid disease risk are discussed. This paper reviews the effects of phytochemicals on thyroid function as well as their possible beneficial or detrimental effects on thyroid disease risk, specifically focusing on hypothyroidism, hyperthyroidism, and thyroid cancers.
... Fischer rat thyroid cells (FRTL) when treated with soy protein and isoflavones; there was a dose dependent suppression of iodide uptake in FRTL cells whereas isoflavone alone was not effective. Soy protein and isoflavone increased nonglycosylated sodium/iodide symporter (NIS) and the 40 kDa thyroglobulin fragment which is a known autoimmunogen in the FRTL cells that potentially contributes to thyroid dysfunction (29). ...
Objective: Soy phytoestrogens are suggested to impair thyroid function but the effects of pharmacological doses of soy phytoestrogens are unknown; therefore, this study was performed to determine the effect of high dose soy phytoestrogens (66 mg) on thyroid function in subclinical hypothyroidism.
Design and setting: Randomized, double-blind, crossover study.
Participants: Forty four patients with subclinical hypothyroidism.
Intervention: Participants were randomly allocated to either 66 mg phytoestrogen with 30 g soy protein (active) or 0 mg phytoestrogen with 30 g soy protein (placebo) supplementation for 8 weeks, washed out for 8 weeks and then crossed over for another 8 week period.
Main outcome measures: The primary outcome was progression to overt hypothyroidism with the secondary outcome measures were changes in thyroid function tests.
Results: Two patients in this trial progressed into overt hypothyroidism after high dose phytoestrogen supplementation. TSH, free thyroxine and triiodothyronine did not differ between groups.
Conclusion: A pharmacological dose of 66 mg of soy phytoestrogens did not increase the overt thyroid failure rate or alter thyroid function tests in patients with subclinical hypothyroidism.
... They found out that the frequency of feedings with soy-based milk formulas in early life was significantly higher in children with autoimmune thyroid diseases (prevalence 31%) as compared with their siblings (prevalence 12% p < 0.01) and healthy nonrelated control children (prevalence 13%, p < 0.02). More recently working in rodent, Tran and co-workers [298] showed that GEN, DAID, or glycitein and a soy extract suppressed iodine uptake and stimulated the production of autoimmunogen in rat thyrocytes in vitro. However, cells were from rat, and the efficient doses were higher than 1 μM. ...
... (29) In vitro studies have demonstrated that isoflavones inhibit thyroid peroxidase (TPO) and inhibit iodide. (30) However, other studies using different preparations for up to 3 years have not shown changes in thyroid hormones. (31) In patients with subclinical hypothyroidism, the soy protein and isoflavone combination has been shown to increase the risk of developing overt hypothyroidism. ...
Background
Hormone replacement therapy may be beneficial for cardiovascular disease risk (CVR) in post-menopausal women. Soy isoflavones may act as selective estrogen receptor modulators. The aim of this study was to evaluate whether soy isoflavones had an effect on CVR markers.
Methods
The expected 10-year risk of cardiovascular disease and mortality were calculated as a secondary endpoint from a double blind randomised parallel study involving 200 women (mean age 55 years, Caucasian, Hull, UK, 2012) in the early menopause who were randomised to 15g soy protein with 66mg isoflavone (SPI) or 15g soy protein alone (depleted of all isoflavones; SP) given as a snack bar between meals daily for 6 months. Age, diabetes, smoking, blood pressure and lipid profiles were used to calculate CVR using the Framingham CVR engine.
Results
SPI treatment resulted in a significant reduction in the metabolic parameters and systolic blood pressure compared to SP (p<0.01). There were no changes in fasting lipid profile and diastolic blood pressure with either treatment. At 6 months, changes in these parameters with SPI treatment were reflected in a calculated 27% (p<0.01) reduction in 10 year coronary heart disease risk, a 37% (p<0.01) reduction in myocardial infarction risk, a 24% (p<0.04) reduction in cardiovascular disease and 42% (p<0.02) reduction in cardiovascular disease death risk.
Conclusions
Supplementation with soy protein with isoflavones for 6 months significantly improved CVR markers and calculated CVR at 6 months during early menopause compared to soy protein without isoflavones.
ISRCTN registry
ISRCTN34051237.
... Small scale study at the impact of 141 mg of dietary isoflavones from soy protein isolate showed no impact on thyroid measurement. Lisa et al. [12] reported that rats feed with soy extract had no inhibitory effect on iodine uptake in albino rats. Additional factor might combine with soy isoflavonoes intake to put the thyroid at added risk. ...
Soy foods are traditional staples of Asian diets. Soy bean and thyroid health have focused on one specific category of nutrient-Isoflavones found in soy bean. This study examined the impact of soy bean on thyroid hormones which are thyroid stimulating hormone (TSH), tri-iodothyronine (T3) and thyroxine (T4) in albino rats. This was carried out in two phases. The rats were grouped in both phases of four groups, three rats in each group. The first phase was by feeding the animals at varying percentage (30, 50 and 70) for two weeks, while the second phase was by administration of soybean extract at (500, 1000 and 2000 mg/kg) respectively for same duration. The result obtained showed that thyroid hormones values for the fed groups were not significantly (p<0.05) different with that of the control group. Also the result obtained for phase two showed that thyroid hormones values of the treated groups were not significantly (p<0.05) different with that of the control group. The result for both phases showed that soy bean has no significant impact on the thyroid hormones levels of albino rates.
... This point is unique; to the best of our knowledge, there have been almost no other reports in which the presence of isoflavone has been examined in patient serum. The other following two mechanisms of hypothyroidism by soybean are considered: (1) An alcohol-soluble component in soybean inhibits iodide uptake [8], and (2) phytic acid salt in soybean chelates the essential minerals, especially zinc, for thyroid hormone production [9,10]. Our patient presented with severe hypothyroidism after 6 months of regular consumption of a health drink. ...
Abstract Background Many people have thyroid conditions that make them susceptible to hypothyroidism. If the foods they eat may interfere with the production of thyroid hormone, which can lead to development of serious hypothyroidism. The danger of health drinks should always be noted. Case presentation A 72-year-old Japanese woman was previously diagnosed with chronic lymphocytic thyroiditis caused by a goiter and had an elevated thyroid-stimulating hormone level (6.56 μIU/ml), a high anti-thyroid peroxidase antibody level (>600 IU/ml), and a high antithyroglobulin level (> 4000 IU/ml) but normal levels of free triiodothyronine (3.08 pg/ml) and thyroxine (1.18 ng/ml). She presented to our hospital with sudden-onset general malaise, edema, and hoarseness with an elevated thyroid-stimulating hormone (373.3 μIU/ml) level and very low triiodothyronine (
... (29) In vitro studies have demonstrated that isoflavones inhibit thyroid peroxidase (TPO) and inhibit iodide. (30) However, other studies using different preparations for up to 3 years have not shown changes in thyroid hormones. (31) In patients with subclinical hypothyroidism, the soy protein and isoflavone combination has been shown to increase the risk of developing overt hypothyroidism. ...
Menopausal estrogen loss leads to an increased bone loss. Soy isoflavones can act as selective estrogen receptor modulators, their role in bone turnover is unclear. The primary outcome was assessing changes in plasma bone turnover markers. The secondary outcomes were assessing changes in cardiovascular risk markers including insulin resistance, blood pressure, and lipid profile. We performed a double-blind randomized parallel study in which 200 women within 2 years after the onset of their menopause were randomized to 15g soy protein with 66mg isoflavone (SPI) or 15g soy protein alone (SP), daily for 6 months. There was a significant reduction in type I collagen crosslinked beta C-telopeptide (βCTX) (bone-resorption marker) with SPI supplementation (0.40±0.17 versus 0.15±0.09μg/L; p<0.01) compared to SP supplementation (0.35±0.12 versus 0.35±0.13μg/L; p=0.92) after 6 months. There was also a significant reduction in type I procollagen-N-propeptide (P1NP) (bone formation marker) with SPI supplementation (50.5±25.0 versus 34.3±17.6μg/L; p<0.01), more marked between 3 and 6 months. Following SPI there was a significant reduction in fasting glucose, fasting insulin, insulin resistance, and systolic blood pressure whereas no significant changes in these parameters was observed with SP. There were no significant changes in fasting lipid profile and diastolic blood pressure with either preparation. There was a significant increase in TSH and reduction in free thyroxine (p<0.01) with SPI supplementation though free tri-iodothyronine was unchanged. In conclusion, soy protein with isoflavones may confer a beneficial effect on bone health, analogous to the mode of action of antiresorptive agents, albeit to a less magnitude. There was a significant improvement of cardiovascular risk markers, but a significant increase in TSH and reduction in free thyroxine after SPI supplementation indicating a detrimental effect on thyroid function.
... Por outro lado, a soja tem gerado preocupação sobre a função da glândula tireoide. 43 Pacientes com hipotireoidismo subclínico apresentam risco três vezes maior de desenvolver hipotireoidismo com suplementação de 16mg fitoestrógenos da soja ao dia. 44 Em estudo realizado com mulheres na menopausa, 45 75mg de isoflavonas reduziram os níveis de T3 livre, bem como aliviaram os sintomas da menopausa. ...
Este artigo teve como objetivo elaborar uma revisão de literatura sobre nutrientes e substâncias alimentares que podem impactar na função tireoidiana. Foi realizada revisão bibliográfica utilizando associação entre os descritores “hipotireoidismo”, “iodo”, “selênio”, “zinco”, “soja”, “glúten” e “flavonoides”, na base de dados Pubmed, em 2014. Foram encontrados 172 artigos e eleitos 42, além de materiais necessários para alcançar o objetivo destse estudo. Observou-se que o iodeto participa da reação de organificação e posteriormente se acopla a resíduos de tirosil para formar os hormônios tireoidianos. Quantidades excessivas ou deficitárias de iodo contribuem para alterações tireoidianas, entre as quais o hipotireoidismo. O selênio e o zinco são cofatores para reações de deiodinação, as quais transformam a tiroxina (T4) em tri-iodotironina (T3) perifericamente. A deficiência desses minerais pode ser desenvolvida em dietas restritivas ou alimentação desequilibrada em qualquer fase da vida, colaborando com a diminuição da produção dos hormônios tireoidianos. Substâncias ingeridas por meio da alimentação, como o tiocianato e o isotiocianato, podem competir com o iodeto pela entrada nos folículos tireoidianos e comprometer a síntese dos hormônios, bem como a soja, que pode inibir a tireoperoxidase, enzima responsável pela oxidação do iodeto e formação dos hormônios tireoidianos, quando há deficiência de iodo. Estudos in vivo que demonstrem o tipo e a quantidade de flavonoides que podem interferir na conversão do T4 em T3 devem ser realizados, bem como estudos para elucidação do papel da isenção do glúten na reversão de hipotireoidismo subclínico.
DOI: 10.12957/demetra.2016.18304
... [214] Also, many studies revealed that there POTENTIAL HEALTH BENEFITS OF SOY ISOFLAVONES is a direct relationship between soy consumption during infancy and autoimmune thyroid disease (ATD) development. [215,216] Tran et al. [217] elucidated anti-thyroid effect of genestein in rat thyrocytes by increasing iodine requirement and inducing the production of P40 which might be responsible for the higher incidence of ATD. ...
Functional foods are the focus of attraction for well-being. The healthy living of Asians may be attributed to a diet enriched with soy isoflavones (SI) viz. genistein and daidzein which fills the gap of proteinaceous diet in vegetarians. Several factors such as administration, dosage, metabolism, ingestion of other pharmacological substances, type of estrogen receptors and presence or absence of endogenous estrogen affect the activities and bioavailability of isoflavones. Mode of therapeutic action could be either through the stimulation of estrogen receptors or by the non-involvement of estrogen receptors. Soy, owing to its isoflavones content serve as a balanced and remedial substitute in combating various lifestyle disorders like cancer prevention by interruption of the breakdown of extracellular matrix that surrounds growing vessels and tumors, lowering of lipid and blood insulin levels by regulating lipid and glucose metabolism, alleviation of menopausal symptoms and osteoprotective effects by modulating estrogen receptors, thus acting as a safer switch to hormone replacement therapy, anti-hypertensive effect which may also contribute to cardioprotective, anti-oxidative effect, regulation of cognitive functions and many others. Therefore, it could be regarded as a valuable therapeutics. However, since SI also act as endocrine disruptors, they also possess some negative effects. Concerns have been raised in relation to thyroid function abnormality. In view of above mentioned facts an attempt has been made to review the literature available on both beneficial as well as deleterious role of isoflavones, soy derived bioactive compounds.
... In addition, there were no significant changes in the levels of Tpo, Tg, Nkx2-1, Foxe1, and Pax8 following exposure to either chemical. Soy extracts have been reported to inhibit iodide uptake, but increase the protein level of non-glycosylated NIS and a 40 kDa Tg fragment in FRTL-5 cells (Tran et al., 2013). Previous reports and the data presented in this study suggest that effects on iodide uptake, TPO activity, and the expression of thyroid specific genes are independent, and each of the chemicals may have different effects on these endpoints. ...
Triclosan, triclocarban, 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), and bisphenol A (BPA) have been reported to disturb thyroid hormone (TH) homeostasis. We have examined the effects of these chemicals on sodium/iodide symporter (NIS)-mediated iodide uptake and the expression of genes involved in TH synthesis in rat thyroid follicular FRTL-5 cells, and on the activity of thyroid peroxidase (TPO) using rat thyroid microsomes. All four chemicals inhibited NIS-mediated iodide uptake in a concentration-dependent manner. A decrease in the iodide uptake was also observed in the absence of sodium iodide. Kinetic studies showed that all four chemicals were non-competitive inhibitors of NIS, with the order of Ki values being triclosan < triclocarban < BDE-47 < BPA. The transcriptional expression of three genes involved in TH synthesis, Slc5a5, Tpo, and Tgo, and three thyroid transcription factor genes, Pax8, Foxe1, and Nkx2-1, was examined using quantitative real-time PCR. No significant changes in the expression of any genes were observed with triclosan or triclocarban. BDE-47 decreased the level of Tpo, while BPA altered the expression of all six genes. Triclosan and triclocarban inhibited the activity of TPO at 166 and > 300 μM, respectively. Neither BDE-47 nor BPA affected TPO activity. In conclusion, triclosan, triclocarban, BDE-47, and BPA inhibited iodide uptake, but had differential effects on the expression of TH synthesis-related genes and the activity of TPO.
... (29) In vitro studies have demonstrated that isoflavones inhibit thyroid peroxidase (TPO) and inhibit iodide. (30) However, other studies using different preparations for up to 3 years have not shown changes in thyroid hormones. (31) In patients with subclinical hypothyroidism, the soy protein and isoflavone combination has been shown to increase the risk of developing overt hypothyroidism. ...
... Much more recently, soya isoflavones were shown to inhibit thyroid peroxidase in vitro and in vivo in rats although rat thyroid function remained normal (26) . Others have reported that in rats while soya isoflavones inhibit synthesis of thyroglobulin and thyroid hormones, availability of thyroid hormone in peripheral tissues may increase (27) . The observation that people living in Asian countries have consumed soya foods for centuries with no perceptible thyrotoxic effects suggests their safety in the general population. ...
Objective:
Consumers may choose soya foods as healthful alternatives to animal products, but concern has arisen that eating large amounts of soya may adversely affect thyroid function. The present study aimed to examine the association between soya food consumption and serum thyroid-stimulating hormone (TSH) concentrations in North American churchgoers belonging to the Seventh-day Adventist denomination that encourages vegetarianism.
Design:
Participants completed six repeated 24 h dietary recalls within a 6-month period. Soya protein and soya isoflavone intakes were estimated, and their relationships to TSH concentrations measured at the end of 6 months were calculated using logistic regression analyses.
Setting:
Calibration sub-study of the Adventist Health Study-2.
Subjects:
Women (n 548) and men (n 295) who were not taking thyroid medications.
Results:
In men, age and urinary iodine concentrations were associated with high serum TSH concentrations (>5 mIU/l), while among women White ethnicity was associated with high TSH. In multivariate models adjusted for age, ethnicity and urinary iodine, soya isoflavone and protein intakes were not associated with high TSH in men. In women higher soya isoflavone consumption was associated with higher TSH, with an adjusted odds ratio (highest v. lowest quintile) of 4·17 (95 % CI 1·73, 10·06). Likewise, women with high consumption of soya protein (midpoint of highest quintile, 11 g/d) v. low consumption (midpoint of lowest quintile, 0 g/d) carried increased odds of high TSH (OR=2·69; 95 % CI 1·34, 5·30).
Conclusions:
In women high consumption of soya was associated with elevated TSH concentrations. No associations between soya intake and TSH were found in men.
... Some herbal products were reported to change thyroid metabolism. Soy consumption is related to thyroid disorders such as hypothyroidism, goiter, and autoimmune thyroid disease besides increased iodine metabolism in animal studies but the exact molecular mechanisms which might be responsible for hypothyroidism is unclear [11]. In our patients, hypothyroidism could not be related to iodine metabolism as both patients were taking levothyroxine. ...
Carum carvi is a widely available herb that has been used as a food additive and as a medication in traditional medicine for many years. Its potential biological effects include analgesic, anti-inflammatory, anti-anxiety and antispasmodic activities. We report a patient with papillary thyroid carcinoma who were under treatment with levothyroxine and experienced an elevated TSH level by ingestion of Carum carvi. TSH level was increased to 60.3mIU/L with no change in levothyroxine dosage and decreased to normal range after discontinuation of the Carum carvi. Observing this dramatic change in TSH level by carum ingestion, carum carvi capsules was produced and one of the researcher tried the medication on herself with a dose of 40 mg/kg/day. She had a history of hypothyroidism and was taking 100 ugr/day of levothyroxine. TSH was markedly increased 2 weeks after ingestion of Carum carvi and returned to normal range 5 months after discontinuation of it. This case report shows the effect of consumption of Carum carvi in increasing TSH level in hypothyroid patients treating with levothyroxine. The exact mechanism of action of carum carvi remains unknown.
... Recently, a study examined the effects of soy isoflavones (ISF) on iodide uptake and expression of thyroglobulin (Tg) and sodium/iodide symporter (NIS) in thyrocytes. This study demonstrated that the alcohol soluble component(s) in soy significantly inhibited iodide uptake in the FRTL cells and that soy ISF, particularly genistein, may increase the incidence of ATD, which is reported in soy infant formula-fed children, by inducing the production of P40, a strong autoimmunogen [86]. ...
Industrial chemical contaminants have a variable impact on the hypothalamic-pituitary-thyroid axis, this depending both on their class and on confounding factors. Today, mounting evidence is pointing to the role of environmental factors, and specifically EDCs, in the current distressing upsurge in the incidence of thyroid disease. The unease is warranted. These substances, which are nowadays rife in our environments (including in foodstuffs), have been shown to interfere with thyroid hormone action, biosynthesis, and metabolism, resulting in disruption of tissue homeostasis and/or thyroid function. Importantly, based on the concept of the "nonmonotonic dose-response curve", the relationship between dose and effect has often been found to be nonlinear. Thus, small doses can induce unpredictable, adverse effects, one case being polychlorinated biphenyls (PCBs), of which congener(s) may centrally inhibit the hypothalamic-pituitary-thyroid axis, or dissociate thyroid receptor and selectively affect thyroid hormone signaling and action. This means that PCBs can act as agonists or antagonists at the receptor level, underlining the complexity of the interaction. This review highlights the multifold activity of chemicals demonstrated to cause thyroid disruption. It also represents a call to action among clinicians to undertake systematic monitoring of thyroid function and registering of the classes of EDs and additionally urges broader scientific collaborations to clarify these chemicals' molecular mechanisms of action, substances whose prevalence in our environments is disrupting not only the thyroid but all life on earth.
It is estimated that more and more couples suffer from fertility and pregnancy maintenance disorders. It is associated with impaired androgen secretion, which is influenced by many factors, ranging from genetic to environmental. It is also important to remember that fertility disorders can also result from abnormal anatomy of the reproductive male and female organ (congenital uterine anomalies-septate, unicornuate, bicornuate uterus; acquired defects of the uterus structure-fibroids, polyps, hypertrophy), disturbed hormonal cycle and obstruction of the fallopian tubes resulting from the presence of adhesions due to inflammation, endometriosis, and surgery, abnormal rhythm of menstrual bleeding, the abnormal concentration of hormones. There are many relationships between the endocrine organs, leading to a chain reaction when one of them fails to function properly. Conditions in which the immune system is involved, including infections and autoimmune diseases, also affect fertility. The form of treatment depends on infertility duration and the patient's age. It includes ovulation stimulation with clomiphene citrate or gonadotropins, metformin use, and weight loss interventions. Since so many different factors affect fertility, it is important to correctly diagnose what is causing the problem and to modify the treatment regimen if necessary. This review describes disturbances in the hormone secretion of individual endocrine organs in the context of fertility and the maintenance of pregnancy.
Exposure to endocrine-disrupting chemicals during critical windows of development may lead to functional abnormalities in adulthood. Isoflavones are a flavonoid group of phytoestrogens that are recognized by their estrogenic activity and are highly abundant in soybean. Since the thyroid gland presents estrogen receptors and infants, toddlers and teenagers may consume isoflavones from soy-based infant formula and beverages as alternatives to animal milk, we propose to investigate the potential effects of relevant concentrations of soy isoflavones in the regulation of the hypothalamic–pituitary (HP) thyroid axis using peripubertal male rats as an experimental model. Thirty-two 23-day-old male rats were exposed to 0.5, 5, or 50 mg of soy isoflavones/kg from weaning to 60 days of age, when they were euthanized, and the tissues were collected to evaluate the mRNA expression of genes involved in the regulation of the HP thyroid axis and dosages of thyroid hormones (THs). Serum TSH concentrations were increased, while alterations were not observed in serum concentrations of triiodothyronine and thyroxine. Regarding mRNA gene expression, Mct-8 was increased in the hypothalamus, Mct-8 , Thra1 , and Thrb2 were decreased in the pituitary, and Nis and Pds were reduced in the thyroid. In the heart, Mct8 and Thrb2 were increased, and Thra1 was decreased. In the liver, Mct8 , Thra1 , and Thrb2 were decreased. These results suggest that the consumption of relevant doses of soy isoflavones during the peripubertal period in males may induce subclinical hypothyroidism, with alterations in the regulation of the HP thyroid axis, modulation of TH synthesis, and peripheral alterations in TH target organs.
Isoflavones are phytoestrogens with recognized estrogenic activity but may also affect testosterone, corticosterone and thyroid hormone levels in experimental models. However, the molecular mechanisms involved in these alterations are still unclear. Isoflavones are present in soy-based infant formula, in breast milk after the consumption of soy by the mother and are widely used for the preparation of beverages consumed by toddlers and teenagers. In this sense, we proposed to investigate the effects of soy isoflavone exposure during the prepubertal period, a recognized window of sensitivity for endocrine disruption, over the hypothalamic-pituitary-testicular (HPT) axis. For this, 42 3-week-old male Wistar rats were exposed to 0.5, 5 or 50 mg of soy isoflavones/kg from postnatal day (PND) 23 to PND60. We evaluated body growth, age at puberty, serum concentrations of LH, FSH, testosterone and estradiol, and the expression of the transcripts (mRNA) of genes encoding key genes controlling the hypothalamic-pituitary-testicular (HPT) axis. In the hypothalamus, we observed an increase in Esr1 mRNA expression (0.5 and 5 mg). In the pituitary, we observed an increase in Gnrhr mRNA expression (50 mg), a reduction in Lhb mRNA expression (0.5 mg), and a reduction in Ar mRNA expression. In the testis, we observed an increase in Lhcgr mRNA expression (50 mg) and a reduction in Star mRNA expression (0.5 and 5 mg). The serum levels of LH (5 and 50 mg) and FSH (0.5 mg) were increased, while testosterone and estradiol were reduced. Puberty was delayed in all groups. Taken together, these results suggest that prepubertal consumption of relevant levels of soy isoflavones disrupts the HPT axis, causing hypergonadotropic hypogonadism and altered expression levels of key genes regulating the axis.
Background:
Phytoestrogens are non-endocrine, non-steroidal secondary derivatives of plants and consumed through plant-based diet also named as "dietary estrogens". The major sources of phytoestrogens are soy and soy-based foods, flax seed, chickpeas, green beans, dairy products, etc. The dietary inclusion of phytoestrogen based foods play a crucial role in the maintenance of metabolic syndrome cluster including obesity, diabetes, blood pressure, cancer, inflammation, cardiovascular diseases, postmenopausal ailments and their complications. In recent days, phytoestrogens are the preferred molecules for hormone replacement therapy. On the other hand, they act as endocrine disruptors via estrogen receptor mediated pathways. These effects are not restricted to adult males or females and identified even in development.
Objective:
Since phytoestrogenic occurrence is high at daily meal for most people from all over the world, they focused to study for its beneficiary effects towards developing pharmaceutical drugs for treating various metabolic disorders by keeping an eye on endocrine disruption.
Conclusion:
The present review emphasizes the pros and cons of phytoestrogens on human health, which may help to direct the pharmaceutical industry to produce various phytoestrongen based drugs against various metabolic disorders.
Soy food health effects are due to isoflavone (ISF) components functioning as phytoestrogens similar to natural estrogen. Epidemiological data suggest a role of estrogens in pathogenesis of thyroid diseases explaining their prevalence in women.
Aim of this study was to determine in vitro effects of isoflavones, soybean extract and Cimicifuga extract on iodide uptake, a crucial step in thyroid hormone biosynthesis, by using a differentiated TSH-dependent cell line (FRTL5).
Estradiol didn’t influence iodide uptake and sodium-iodide symporter (NIS) mRNA expression in FRTL-5 cells. None of analyzed glycoside or aglycone isoflavone determined a significant inhibition of iodide uptake, while both isoflavone rich and triterpene rich extracts determined a significant reduction of iodide uptake at the higher doses.
While soybean and Cimicifuga extracts inhibited iodide uptake at high doses, none of analyzed isoflavone exerted this effect. These elevated doses, however, are never reached in the blood following intake of food supplements.
Context:
Isoflavones found in soy products have a chemical structure similar to estrogen, leading to concerns of an adverse estrogenic effect in men, particularly in those with type 2 diabetes mellitus (T2DM) who have low testosterone levels due to hypogonadism.
Objective:
The primary outcome was change in total testosterone levels. The secondary outcomes were the changes in glycaemia and cardiovascular risk markers.
Design:
Randomised double blind parallel study.
Setting:
Secondary care setting in UK.
Participants:
200 men with T2DM with a total testosterone level≤12nmol/L Intervention: 15g soy protein with 66mg of isoflavones (SPI) or 15g soy protein alone without isoflavones (SP) daily as snack bars for three months.
Results:
There was no change in either total testosterone or in absolute free testosterone levels with either SPI or SP. There was an increase in TSH and reduction in fT4 (p<0.01) after SPI supplementation. Glycaemic control improved with a significant reduction in HbA1c (-4.19(7.29)mmol/mol,p<0.01) and HOMA-IR after SPI. Cardiovascular risk improved with a reduction in triglycerides, CRP and diastolic BP (p<0.05) with SPI versus SP supplementation. There was 6% improvement in 10-year coronary heart disease risk after three months of SPI supplementation. Endothelial function improved with both SPI and SP supplementation (p<0.01) with an increased reactive hyperemia index that was greater for the SPI group (p<0.05).
Conclusions:
Testosterone levels were unchanged and there was a significant improvement in glycaemia and cardiovascular risk markers with SPI compared to SP alone over three months. There was significant increase in TSH and a reduction in fT4.
There are many combinations of drug-drug interactions that have been extensively cited in the literature; on the other hand different food-drug interactions exist and can have serious negative effects on health which must not be discarded. During the present review different points were discussed including effect of drug administration on food utilization, nutritional status and appetite such as effect of drug on eating behavior or macronutrient specific dietary selection and nutrients absorption and metabolism. Effect of drug on vitamin needs, nutrient-nutrient incompatibilities, impact of anti-inflammatory drugs on nutritional status and effect of slimming drugs on serum minerals during consumption of different food were reviewed. Also, effect of the food consumed and nutritional status on the efficiency of drugs was dealt with; such as influence of the type of food, malnutrition and obesity on drug absorption, blood levels and efficiency. Nutritional effect on drug-protein binding in plasma, systemic reactions induced by drug-food incompatibilities and effect of different nutrients on drug biotransformation were discussed. Among the important points which were reviewed id to what extent the consumption of food or nutrient may affect the drug dosage. The present review highlighted the various bioactive components of food that possess medicinal effect.
Vitiligo is a pigmentary disorder strongly associated with autoimmune thyroid disorders (ATD). Thyroid hormones antibodies (THAb) directed toward thyroxine (T3) and triiodothyronine (T4) (T3- and T4-Ab) are rare in the general population but are increased in individuals wit ATD and extrathyroid autoimmune disorders. Because it is known that alcohol, smoke, iodine, and some thyroid disruptors can elicit the appearance of ATD, the aim of our study was to evaluate possible correlation between T3- and T4-Ab expression and past toxic exposures in vitiligo patients. Seventy vitiligo patients were examined and self-reported exposure to thyroid disruptors (4,4'-isopropylidenediphenol, perchlorates, polychlorinated biphenyls (PCBs), hexachlorobenzene, resorcinol, dichlorodiphenyltrichloroethane, alachlor/amitriole, nitrate, thiocyanate, soy isoflavones), iodine intake, smoke, and alcohol consumption were investigated through standardized questionnaires. Immunoglobulin (Ig)M-T3-Ab, IgG-T3-Ab, IgM-T4-Ab,and IgG-T4-Ab were dosed by a radioimmunoprecipitation technique. Seventy-seven (95.7 %) patients had at least one type of THAb. Most of them had contemporarily both T3- and T4-Ab (50/70). We found a significant association between PCBs and T4-IgG-Ab (P = 0.039) and between food intake containing nitrate, thiocyanate, and soy isoflavones with (IgM + IgG)-T3-Ab (P = 0.041). Our study underlines a possible influence of diet and environment in vitiligo patients in eliciting THAb. Therefore, in the event of a positive exposure to thyroid disruptors, an evaluation of thyroid function might be useful to early detect possible associated thyroid autoantibodies such as THAb.
Thyroid carcinogenesis is accompanied by loss of thyroid-specific functions and refractory to radioiodine and thyroid stimulating hormone (TSH) suppression therapy. Redifferentiating agents have been shown to inhibit tumor growth and improve the response to conventional therapy. Polyphenol phytochemicals (PPs) in fruits and vegetables have been reported to inhibit cancer initiation, promotion, progression and induce redifferentiation in selected types. In this study we examined PPs induce redifferentiation in thyroid cancer cell lines. We investigated the effects of genistein, resveratrol, quercetin, kaempferol, and resorcinol on the F9 embryonal carcinoma cell differentiation model. The thyroid cancer cell lines, TPC-1, FTC-133, NPA, FRO, and ARO, displayed growth inhibition in response to genistein, resveratrol, quercetin. We further demonstrated that genistein decreased the dedifferention marker CD97 in NPA cells and resveratrol decreased CD97 in FTC-133, NPA, FRO cells and quercetin decreased CD97 in all cell lines. We observed increased expression of differentiation marker NIS in FTC-133 cells in response to genistein, and resveratrol but no change in NPA, FRO, ARO cells. Quercetin increased or induced NIS in FTC-133, NPA, FRO cells. These findings suggest that PPs may provide a useful therapeutic intervention in thyroid cancer redifferentiation therapy.
The potential role of genistein in the prevention and treatment of obesity has attracted much attention among public and medical communities. Conversely, increasing evidence indicates that genistein as an endocrine-disrupting substance is likely to play a role in the aetiology of obesity. This review focuses on the role of soy phyto-oestrogen genistein in adipocytes and the underlying mechanisms of action. Genistein dose-dependently inhibits and stimulates adipogenesis in vitro. Increasing evidence shows that genistein dose-dependently influences obesity in both male and female animals. Dose-dependent effects of genistein on adipocytes vary with factors such as age and gender of animals. In addition, the role of developmental exposure of genistein in adult obesity has been discussed. Genistein, different from oestrogen, concurrently activates nuclear receptors, oestrogen receptors and peroxisome proliferator-activated receptors, and it inhibits various enzyme activities. The balance among these pleiotrophic effects of genistein determines its dose-dependent effects on adipocyte differentiation and function. Current data suggest that genistein could regulate adiposity. However, it remains uncertain whether genistein plays a beneficial role in the prevention and treatment of obesity. Additional evidence is required before firm conclusions showing that genistein decreases adiposity.
The Na+/I- symporter (NIS) is the plasma membrane protein that catalyzes active I- transport in the thyroid, the first step in thyroid hormone biogenesis. The cDNA encoding NIS was recently cloned in our laboratory and a secondary structure model proposed, suggesting that NIS is an intrinsic membrane protein (618 amino acids; approximately 65.2 kDa predicted molecular mass) with 12 putative transmembrane domains. Here we report the generation of a site-directed polyclonal anti-COOH terminus NIS antibody (Ab) that immunoreacts with a approximately 87 kDa-polypeptide present in membrane fractions from a rat thyroid cell line (FRTL-5). The model-predicted cytosolic-side location of the COOH terminus was confirmed by indirect immunofluorescence experiments using anti-COOH terminus NIS Ab in permeabilized FRTL-5 cells. Immunoreactivity was competitively blocked by the presence of excess synthetic peptide. Treatment of membrane fractions from FRTL-5 cells, Xenopus laevis oocytes, and COS cells expressing NIS with peptidyl N-glycanase F converted the approximately 87 kDa-polypeptide into a approximately 50 kDa-species, the same relative molecular weight exhibited by NIS expressed in E. coli. Anti-NIS Ab immunoprecipitated both the NIS precursor molecule (approximately 56 kDa) and the mature approximately 87 kDa form. Furthermore, a direct correlation between circulating levels of thyroid-stimulating hormone and NIS expression in vivo was demonstrated.
The rat, mouse and human estrogen receptor (ER) exists as two subtypes, ER alpha and ER beta, which differ in the C-terminal ligand-binding domain and in the N-terminal transactivation domain. In this study, we investigated the estrogenic activity of environmental chemicals and phytoestrogens in competition binding assays with ER alpha or ER beta protein, and in a transient gene expression assay using cells in which an acute estrogenic response is created by cotransfecting cultures with recombinant human ER alpha or ER beta complementary DNA (cDNA) in the presence of an estrogen-dependent reporter plasmid. Saturation ligand-binding analysis of human ER alpha and ER beta protein revealed a single binding component for [3H]-17beta-estradiol (E2) with high affinity [dissociation constant (Kd) = 0.05 - 0.1 nM]. All environmental estrogenic chemicals [polychlorinated hydroxybiphenyls, dichlorodiphenyltrichloroethane (DDT) and derivatives, alkylphenols, bisphenol A, methoxychlor and chlordecone] compete with E2 for binding to both ER subtypes with a similar preference and degree. In most instances the relative binding affinities (RBA) are at least 1000-fold lower than that of E2. Some phytoestrogens such as coumestrol, genistein, apigenin, naringenin, and kaempferol compete stronger with E2 for binding to ER beta than to ER alpha. Estrogenic chemicals, as for instance nonylphenol, bisphenol A, o, p'-DDT and 2',4',6'-trichloro-4-biphenylol stimulate the transcriptional activity of ER alpha and ER beta at concentrations of 100-1000 nM. Phytoestrogens, including genistein, coumestrol and zearalenone stimulate the transcriptional activity of both ER subtypes at concentrations of 1-10 nM. The ranking of the estrogenic potency of phytoestrogens for both ER subtypes in the transactivation assay is different; that is, E2 > zearalenone = coumestrol > genistein > daidzein > apigenin = phloretin > biochanin A = kaempferol = naringenin > formononetin = ipriflavone = quercetin = chrysin for ER alpha and E2 > genistein = coumestrol > zearalenone > daidzein > biochanin A = apigenin = kaempferol = naringenin > phloretin = quercetin = ipriflavone = formononetin = chrysin for ER beta. Antiestrogenic activity of the phytoestrogens could not be detected, except for zearalenone which is a full agonist for ER alpha and a mixed agonist-antagonist for ER beta. In summary, while the estrogenic potency of industrial-derived estrogenic chemicals is very limited, the estrogenic potency of phytoestrogens is significant, especially for ER beta, and they may trigger many of the biological responses that are evoked by the physiological estrogens.
Here, we studied the fragmentation of the prothyroid hormone, thyroglobulin (Tg), which occurs during thyroid hormone synthesis, a process which involves iodide, thyroperoxidase, and the H2O2-generating system, consisting of glucose and glucose oxidase. Various peptides were found to be immunoreactive to autoantibodies to Tg from patients and monoclonal antibodies directed against the immunodominant region of Tg. The smallest peptide (40 kDa) bore thyroid hormones and was identified at the C-terminal end of the Tg molecule, which shows homologies with acetylcholinesterase. Similar peptides were obtained by performing metal-mediated oxidation of Tg via a Fenton reaction. It was concluded that the oxidative stress induced during hormone synthesis generates free radicals, which, in turn, cleave Tg into immunoreactive peptides.
Transformation of rat thyroid cells with polyoma virus middle T antigen results in loss of the thyroid-differentiated phenotype, measured as the expression of the thyroglobulin (Tg), thyroperoxidase (TPO), and sodium/iodide symporter (NIS) genes. Among the transcription factors involved in the regulation of these genes, TTF-1 and TTF-2 were still detected at nearly wild-type levels, while a specific loss of the paired domain transcription factor Pax8 was observed. In this study, we used the PCPy cell line as a model system to study the role of Pax8 in thyroid differentiation. We demonstrate that the reintroduction of Pax8 in PCPy cells is sufficient to activate expression of the endogenous genes encoding thyroglobulin, thyroperoxidase, and sodium/iodide symporter. Thus, this cell system provides direct evidence for the ability of Pax8 to activate transcription of thyroid-specific genes at their chromosomal locus and strongly suggests a fundamental role of this transcription factor in the maintenance of functional differentiation in thyroid cells. Moreover, we show that Pax8 and TTF-1 cooperate in the activation of the thyroglobulin promoter and that additional thyroid-specific mechanism(s) are involved in such a cooperation. To identify the Pax8 domain able to mediate the specific activation of the thyroglobulin promoter, we transfected in PCPy cells three different Pax8 isoforms. The results of such experiments indicate that for the transcriptional activation of thyroid-specific genes, Pax8 uses an as yet unidentified functional domain.
We recently reported that, during in vitro thyroid-hormone synthesis, H(2)O(2) stress cleaved thyroglobulin (Tg) into C-terminal peptides. These peptides were found to contain the immunodominant region of Tg recognized by Tg autoantibodies from patients with an autoimmune thyroid disease. To test the hypothesis that Tg fragmentation is an early upstream initiating event involved in Tg autoimmune response and the consequence of oxidative injuries, we studied the effect of H(2)O(2) stress on human thyroid cells. In culture conditions allowing Tg synthesis and iodine organification by the cells, we found that bolus addition of increasing millimolar doses of H(2)O(2) induced a dose-response appearance of floating cells in the culture medium. These cells apparently resulted from a necrotic process, and they bore iodinated Tg fragments. These fragments were found to be similar to those previously obtained in vitro from purified Tg. In both cases, Tg peptides were recognized by a well-defined monoclonal antibody directed to the immunodominant region of Tg. The smallest immunoreactive Tg peptide had a molecular mass of 40 kDa and entered human thyrocytes more efficiently than the entire Tg. These data suggest that thyrocytes exposed to locally increased H(2)O(2) doses accumulate fragmented Tg for further delivery into surrounding living thyrocytes in the course of an autoimmune response.
The long-term clinical effects of soy protein containing various concentrations of isoflavones on endogenous hormones are unknown.
We examined the effects of ingestion of soy protein containing various concentrations of isoflavones on hormone values in postmenopausal women.
Seventy-three hypercholesterolemic, free-living, postmenopausal women participated in a 6-mo double-blind trial in which 40 g protein as part of a National Cholesterol Education Program Step I diet was provided as casein from nonfat dry milk (control), isolated soy protein (ISP) containing 56 mg isoflavones (ISP56), or ISP containing 90 mg isoflavones (ISP90). Endogenous hormone concentrations were measured at baseline and at 3 and 6 mo.
The concentration of thyroxine and the free thyroxine index were higher in the ISP56 group, and the concentration of thyroid-stimulating hormone was higher in the ISP90 group than in the control group at 3 and 6 mo (P < 0.05). Triiodothyronine was significantly higher in the ISP90 group only at 6 mo. Thyroxine, free thyroxine index, and thyroid-stimulating hormone at 6 mo were inversely associated with measures of baseline estrogenicity. No significant differences were found for endogenous estrogens, cortisol, dehydroepiandrosterone sulfate, insulin, glucagon, or follicle-stimulating hormone after baseline hormone values were controlled for.
This study does not provide evidence that long-term ingestion of soy protein alters steroid hormone values, but it suggests that soy protein may have small effects on thyroid hormone values that are unlikely to be clinically important. The thyroid effects are, however, consistent with previous findings in animals and highlight the need for future research investigating possible mechanisms of action.
Phyto-oestrogens are non-steroidal plant-derived compounds that possess oestrogenic activity and act as selective oestrogen receptor modulators (SERMs). Among the dietary oestrogens, the isoflavone class enjoy a wide-spread distribution in most of the members of the Leguminosae family, including such prominent high-content representatives as soybean. Phyto-oestrogen research has grown rapidly in recent years owing to epidemiological studies suggesting that diets rich in soy may be associated with potential health benefits. There is a paucity of data on endocrine effects of soy phytochemicals during infancy, the most sensitive period of life for the induction of toxicity. The safety of isoflavones in infant formulas has been questioned recently owing to reports of possible hormonal effects. Infants fed soy formula receive high levels of phyto-oestrogens in the form of isoflavones (genistein, daidzein and their glycosides). To date, no adverse effects of short- or long-term use of soy proteins have been observed in humans and exposure to soy-based infant formulas does not appear to lead to different reproductive outcomes than exposure to cow milk formulas. Soy formula seems to be a safe feeding option for most infants. Nevertheless, much closer studies in experimental animals and human populations exposed to phyto-oestrogen-containing products, and particularly soy-based infant formulas, are necessary.
Thyroid hormone receptors (TRs) are regulators of many genes involved in cholesterol and lipid metabolism. The purpose of this study was to examine the effect of soy protein isolate (SPI) and isoflavones on hepatic TRs in rats. In Expt. 1, Sprague-Dawley rats were fed diets containing either casein or alcohol-washed SPI with or without isoflavone supplementation (5-1250 mg/kg diet) for 70, 190, and 310 d. The offspring (F1) were fed the same diets as their parents (F0). In Expt. 2, Sprague-Dawley rats were fed diets containing casein or casein plus isoflavones (50-400 mg/kg diet) for 120 d. The mRNA and protein contents of the hepatic TRs were measured by semiquantitative RT-PCR and Western blot, respectively. TRalpha1, TRalpha2, and TRbeta2 contents were not affected by SPI. However, the content of the 52-kDa TRbeta1 protein, the major isoform present in the liver, was markedly increased by dietary SPI in both sexes of F0 and F1 compared with casein. The supplemental isoflavones had no effect on TRbeta1, whereas the high doses of isoflavones (250 and 1250 mg/kg diet) reduced the hepatic TRalpha1 protein content in F1 male rats on d 28. SPI had no effect on total T3 and T4 levels. However, higher dose of supplemental isoflavones markedly increased T4 level in female rats. Overall, this study demonstrates for the first time that SPI upregulates hepatic TRbeta1 expression, and that isoflavones reduce the hepatic TRalpha1 level in young male rats. The SPI-induced TRbeta1 may play a role in mediating the hypocholesterolemic and lipid-lowering actions of soy protein.
Our previous studies showed that intake of 20% alcohol-washed soy protein isolate (SPI) significantly increased hepatic thyroid hormone receptor (TR) beta1 protein content in rats. However, whether SPI influences the binding ability of TR to its target genes is unknown. The purpose of this study was to examine the effect of increasing amounts of dietary SPI on hepatic TRbeta1 content and the binding of TR to thyroid hormone response element (TRE) in rats. Sprague-Dawley rats (28 d old) were fed diets containing casein (20%) with or without isoflavone supplementation (50 mg/kg diet) or alcohol-washed SPI (5, 10, or 20%) for 90 d. The hepatic TRbeta1 protein content was measured by Western blot, and the binding ability of TR to DNA was examined by electrophoretic mobility shift assay. Consumption of the 20% SPI diet increased pancreatic relative weight and decreased spleen relative weight. Intake of SPI markedly elevated TRbeta1 content in both male and female rats compared with a casein-based control diet. The increase in TRbeta1 in females was much higher than that in males. Interestingly, the binding abilities of TR to DNA were significantly inhibited by increasing amounts of dietary SPI in female rats. In conclusion, this study shows for the first time that dietary SPI increases hepatic TRbeta1 protein content and inhibits the binding of TR to target genes. Modulation of hepatic TRbeta1, a key regulator of gene expression involved in lipid metabolism, by SPI may be a novel mechanism by which soy components lower blood lipid level and exert their hypocholesterolemic actions.
Soy protein-based formulas have been available for almost 100 years. Since the first use of soy formula as a milk substitute for an infant unable to tolerate a cow milk protein-based formula, the formulation has changed to the current soy protein isolate. Despite very limited indications for its use, soy protein-based formulas in the United States may account for nearly 25% of the formula market. This report reviews the limited indications and contraindications of soy formulas. It will also review the potential harmful effects of soy protein-based formulas and the phytoestrogens contained in these formulas.
Genistein, a natural isoflavone phytoestrogen present in soybeans, caused a dose-dependent growth inhibition of the two hormone-sensitive cell lines T47D and ZR75.1 and of the two hormone-independent cell lines MDAMB-231 and BT20. Flow cytometric analysis of cells treated for 4 days with 15 and 30 μM genistein showed a dose-dependent accumulation in the G2M phase of the cell cycle. At the highest tested concentration, there was a sevenfold increase in the percentage of cells in G2M (63%) with respect to the control (9%) in the case of T47D cells and a 2.4-fold increase in the case of BT20. An intermediate fourfold accumulation was observed in the case of MDAMB-231 and ZR75.1. The G2M arrest was coupled with a parallel depletion of the G0/G1 phase. To understand the mechanism of action underlying the block in G2M induced by genistein, we investigated the expression and the activity of cyclins and of cyclin-dependent kinases specifically involved in the G2→M transition. As expected, p34cdc-2 expression, monitored by Western blotting, was unaffected by genistein treatment in all cell lines. With exception of the T47D cell line, we revealed an increase in the tyrosine phosphorylated form of p34, suggesting an inactivation of the p34cdc-2 catalytic activity consequent to treatment of cells with genistein. In fact, immunoprecipitates from genistein-treated MDAMB-231 and BT20 cells displayed a fourfold decrease in kinase activity evaluated using the histone H1 as substrate. Conversely, no variation in kinase activity was observed between treated and untreated ZR75.1 cells despite the increase in p34 phosphorylation. In cells treated with 30 μM genistein, cyclin B1 (p62) increased 2.8-,8-and 103-fold, respectively, in BT20, MDAMB-231, and ZR75.1 cells, suggesting an accumulation of the p62, which is instead rapidly degraded in cycling cells. No effects were observed on cyclin expression in T47D cells. We therefore conclude that genistein causes a G2M arrest in breast cancer cell lines, but that such growth arrest is not necessarily coupled with deregulation of the p34cdc-2/cyclin B1 complex only in all of the studied cell lines. J. Cell. Biochem. 79:594–600, 2000. © 2000 Wiley-Liss, Inc.
Rats were fed iodine-deficient rations (0.7–2.3 μg. iodine /100 g. diet) based upon raw soybeans, solvent-extracted soy Hour, isolated soy proteins, or soybean infant formulas with or without added iodide.Significant enlargement of the thyroid gland occurred on the iodine-deficient rations in 1 or 2 weeks. The addition of 160 μg. iodine as KI /100 g. diet caused the hypertrophied gland to return to normal size in 2 or 3 weeks.Although the lack of iodine is the principal cause of soybean goiter, raw soybeans, which contain more iodine than either solvent -extracted soy flour or glycinin, produce greater thyroid hypertrophy. This observation suggests that raw soybeans have a goitrogenic activity (goitrogen?) which is removed or destroyed during processing.The methodology used to estimate the iodoamino acids in serum and in thyroid digests is discussed. Evidence is presented that neither thiouracil nor propylthiouracil, added as a preservative to serum, is responsible for the reported presence of appreciable quantities of iodotyrosines in rat and human sera.The quantities and distribution of the iodoamino acids in the sera and in digests of the thyroid glands were used as additional criteria to study the changes produced by soybean, goiter and its prevention by the inclusion of KI in the iodine-deficient regimens.Besides the very marked decrease in organic iodine in the serum and in the thyroid glands of the animals on the iodine-deficient rations, the ratios of iodotyrosines to iodothyronines differed from those found in rats receiving soybean diets with added KI or from those on the usual laboratory foods. Thus the ratio of iodotyrosines to iodothyronines in the sera of animals on iodine-deficient diets is approximately 1:1, while it is in the range of 1:2 or 1:4 in the sera of animals containing an adequate, quantity of KI. The situation with respect to the distribution of iodoamino acids in digests of the glands is reversed from that of the serum. In this case, the ratio of iodotyrosines to iodothyronines is much higher in thyroid glands of euthyroid rats than in the glands from iodine-deficient animals. Tentative explanations of these changes in the distribution of iodoamino acids are offered.
There is increasing concern that exposure to flavonoids may lead to endocrine disruption of the hypothalamus–pituitary–thyroid hormone axis, and, additionally, there is evidence that secondary plant metabolites contained in our daily diet or used for hormone-replacement therapy act as hormones themselves, similar to known isoflavonoid effects in the steroid hormone network. These compounds of natural origin affect the thyroid hormone feedback system by interference with different components of this homeostatically regulated system: biosynthesis, secretion and metabolism, transport, distribution, and action of thyroid hormones including the feedback mechanism. Genistein and daidzein, the major components of soy, influence thyroid hormone synthesis by inhibition of the iodide oxidizing enzyme thyroperoxidase, interfere with thyroid hormone transport proteins and 5′-deiodinase type I activities in peripheral tissues, which leads to altered thyroid hormone action at the cellular level. Synthetic flavonoids, such as F21388, structurally similar to thyroxine, cross the placenta and reach the fetal brain of animal models also.
The soy-derived phytoestrogen genistein (GEN) has received attention for its potential benefits on the cardiovascular system by providing direct protection to cardiomyocytes against pathophysiological stresses. Here, we employed a proteomic approach to study the concentration-dependent effects of GEN treatments on cardiomyocytes. Cultured HL-1 cardiomyocytes were treated with low (1μM) and high (50μM) concentrations of GEN. Proteins were pre-fractionated by sequential hydrophilic/hydrophobic extraction and both protein fractions from each treatment group were separated by 2D gel electrophoresis (2DE). Overall, approximately 2,700 spots were visualized on the 2D gels. Thirty-nine and 99 spots changed in volume relative to controls (p<0.05) following the low- and high-concentration GEN treatments, respectively. From these spots, 25 and 62 protein species were identified by ESI-MS/MS and Mascot database searching, respectively. Identified proteins were further categorized according to their functions and possible links to cardioprotection were discussed. MetaCore gene ontology analysis suggested that 1μM GEN significantly impacted the anti-apoptosis process, and that both the low and high concentrations of GEN influenced the glucose catabolic process and regulation of ATPase activity. This proteomics study provides the first global insight into the molecular events triggered by GEN treatment in cardiomyocytes.
The thyroid follicular cell type is devoted to the synthesis of thyroid hormones. Several genes, whose protein products are essential for efficient hormone biosynthesis, are uniquely expressed in this cell type. A set of transcriptional regulators, unique to the thyroid follicular cell type, has been identified as responsible for thyroid specific gene expression; it comprises three transcription factors, named TTF-1, TTF-2, and Pax8, each of which is expressed also in cell types different from the thyroid follicular cells. However, the combination of these factors is unique to the thyroid hormone producing cells, strongly suggesting that they play an important role in differentiation of these cells. An overview of the molecular and biological features of these transcription factors is presented here. Data demonstrating that all three play also an important role in early thyroid development, at stages preceding expression of the differentiated phenotype, are also reviewed. The wide temporal expression, from the beginning of thyroid organogensis to the adult state, is suggestive of a recycling of the thyroid-specific transcription factors, that is, the control of different sets of target genes at diverse developmental stages. The identification of molecular mechanisms leading to specific gene expression in thyroid cells renders this cell type an interesting model in which to address several aspects of cell differentiation and organogenesis.
The standard assay for sodium iodide symporter (NIS) function is based on the measurement of radioiodide uptake ((125)I) in NIS-expressing cells. However, cost and safety issues have limited the method from being used widely. Here we describe a simple spectrophotometric assay for the determination of iodide accumulation in rat thyroid-derived cells (FRTL5) based on the catalytic effect of iodide on the reduction of yellow cerium(IV) to colorless cerium(III) in the presence of arsenious acid (Sandell-Kolthoff reaction). The assay is fast and highly reproducible with a Z' factor of 0.70. This procedure allows the screening of more than 800 samples per day and can easily be adapted to robotic systems for high-throughput screening of NIS function modulators. Using this method, the potency of several known inhibitors of NIS function was evaluated in a single day with high accuracy and reliability. Measured IC(50) values were essentially identical to those determined using Na(125)I.
The sodium iodide symporter (NIS) mediates iodide uptake into the thyroid. Because of this mechanism, differentiated thyroid cancer is susceptible for radioiodine therapy. Functional NIS expression in extrathyroidal tumors has been reported mainly in breast cancer. We screened colorectal tumors for NIS expression and investigated the mechanisms regulating NIS activity. Cell lines were screened for iodide uptake in vitro and NIS expression was evaluated by real-time RT-PCR, immunocytochemistry and immunoblotting. Iodide and pertechnetate uptake were evaluated in allograft tumors by biodistribution studies and scintigraphy. Tumors of transgenic mouse models for colorectal cancer harboring mutations in the oncogenes KRAS, beta-catenin or the tumor-suppressor gene adenomatous-polyposis coli (APC) were screened for NIS expression by RT-PCR. In vitro, functional NIS activity was detected in murine CMT93 rectal carcinoma cells and NIS expression was verified on mRNA and protein level. Inhibition of tyrosine kinases increased iodide uptake. Inhibition of tyrosine phosphatases decreased iodide uptake. In vivo, functional NIS expression was preserved in CMT93 tumors and tumor uptake could be enhanced by treatment of mice with tyrosine kinase inhibitors. In transgenic murine models of colorectal cancer, 14% of endogenous tumors expressed elevated levels of NIS mRNA. We conclude that NIS is functionally expressed in a subset of murine colorectal tumors and its activity is regulated by tyrosine phosphorylation. Therefore, with specific tyrosine kinase inhibition, these tumors might be susceptible for radioiodine treatment. Further studies are justified to identify the specific pathways regulating NIS activity and to transfer these findings to human cell lines and tissues.
A deranged differentiation is often a landmark of transformed cells. We used a thyroid cell line expressing an inducible Ras oncoprotein in order to study the hierarchy of molecular events leading to suppression of thyroid-specific gene expression. We find that, upon Ras activation, there is an immediate global down-regulation of thyroid differentiation, which is associated with an inhibition of the cAMP signaling pathway. We demonstrate that an unusual negative cross talk between Ras oncogene and the cAMP pathway induces inactivation of the transcription factor Pax8 that we propose as a crucial event in Ras-induced dedifferentiation.
TSH stimulation of sodium iodide symporter (NIS) expression in thyroid cancer promotes radioiodine uptake and is required to deliver an effective treatment dose. Activation of the insulin/phosphoinositide-3-kinase (PI3K) signaling pathway in TSH-stimulated thyroid cells reduces NIS expression at the transcriptional level. We, therefore, investigated the effects of PI3K pathway inhibition on iodide uptake and NIS expression in rat thyroid cell lines and human papillary thyroid cancer cells. A PI3K inhibitor, LY294002, significantly enhanced iodide uptake in two rat thyroid cell lines, FRTL-5 and PCCL3. The induction of Nis mRNA by LY294002 occurred 6 h after treatment, and was abolished by a translation inhibitor, cycloheximide. Expression of the transcription factor, Pax8, which stimulates NIS expression, was significantly increased in PCCL3 cells after LY294002 treatment. Removal of insulin abrogated the stimulatory effects of LY294002 on NIS mRNA and protein expression, but not on iodide uptake. These findings suggest that PI3K pathway inhibition results in post-translational stimulation of NIS. Inhibition of the PI3K pathway also significantly increased iodide uptake ( approximately 3.5-fold) in BHP 2-7 papillary thyroid cancer cells (Ret/PTC1 positive), engineered to constitutively express NIS. Pharmacological inhibition of Akt, a factor stimulated by the PI3K pathway, increased exogenous NIS expression in BHP 2-7 as was seen with LY294002, but not increase the endogenous NIS expression in FRTL-5 cells. PI3K pathway inhibition increases functional NIS expression in rat thyroid cells and some papillary thyroid cancer cells by several mechanisms. PI3K inhibitors have the potential to increase radioiodide accumulation in some differentiated thyroid cancer.
Antioxidant and antipromotional effects of the soybean isoflavone genistein have been studied in HL-60 cells and the mouse skin tumorigenesis model. Effects of structure-related flavone/isoflavones on hydrogen peroxide (H2O2) production by 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated HL-60 cells and superoxide anion (O2-) generation by xanthine/xanthine oxidase were compared. Of tested isoflavones, genistein is the most potent inhibitor among TPA-induced H2O2 formation by (dimethyl sulfoxide) DMSO-differentiated HL-60 cells, daidzein is second, and apigenin and biochanin A show little effect. In contrast, genistein, apigenin, and prunectin are equally potent in inhibiting O2- generation by xanthine/xanthine oxidase, with daidzein showing a moderate inhibitory effect and biochanin A exhibiting no effect. These results suggest that the antioxidant properties of isoflavones are structurally related and the hydroxy group at Position 4' is crucial in both systems. Dietary administration of 250 ppm genistein for 30 days significantly enhances the activities of antioxidant enzymes in the skin and small intestine of mice. Further studies show that genistein significantly inhibits TPA-induced proto-oncogene expression (c-fos) in mouse skin in a dose-dependent manner. In a two-stage skin carcinogenesis study, low levels of genistein (1 and 5 mumol) significantly prolong tumor latency and decrease tumor multiplicity by approximately 50%. We conclude that genistein's antioxidant properties and antiproliferative effects may be responsible for its anticarcinogenic effect. Its high content in soybeans and relatively high bioavailability favor genistein as a promising candidate for the prevention of human cancers.
The three isozymes catalyzing deiodination of thyroid hormones and iodothyronines derived thereof exert a major role in tissue- and development-specific expression of thyroid hormone action in target tissues by activating the prohormone T4 to thyromimetically active T3 or by inactivating the prohormone T4 or active T3 in non-target tissues at inappropriate time points. These three isozymes, in cooperation with the enzymes responsible for non-deiodinative degradation of iodothyronines, thus act as "guardians of the gate" to nuclear thyroid hormone receptors and other cellular target sites for thyroid hormone action. Strict and distinct hormonal, nutritional and nerval regulation of expression of the deiodinase isozymes warrants a closely coordinated control of thyroid hormone action, which directs growth, differentiation, and basal metabolic functions in the developing and the adult organism both in the periphery and in the central nervous system. The integrative action of this essential homeostatic and dynamic ancient hormone system in higher vertebrates is under the influence of two essential trace elements, iodine and selenium, which both are inadequately available for man and life stock in great parts of the world. As soon as, and only if, iodine supplementation is achieved, attempts to establish adequate selenium supply for thyroid hormone synthesis, activation, metabolism and action should be made, but not the other way around. In this review, the physiological, biochemical and pharmacological properties of the three deiodinase isozymes are discussed in detail, with special attention to the role of selenium in regulation of type I 5'-deiodinase expression. The contribution of each deiodinase izozyme to the activation and inactivation of thyroid hormones in specific tissues is reviewed.
To assess the etiology of hyperthyroxinemia or hyperthyrotropinemia in infants with congenital hypothyroidism who are on replacement therapy with L-thyroxine.
These infants were treated with recommended doses of L-thyroxine following the diagnosis of congenital hypothyroidism. Because of hyperthyroxinemia (2 patients) and hyperthyrotropinemia (1 patient), medication compliance and dietary practice (formula type, age of introduction, and discontinuation or change of the formula) were assessed. Clinical evaluation was also performed.
Elevated thyroxine level in 2 infants was associated with discontinuation of soy formula 4 weeks previously; reduction of L-thyroxine dose normalized serum levels in both of these infants. In the third infant, who received soy formula from 1 week of age, TSH remained elevated despite incremental L-thyroxine doses of 19 micrograms/kg/day; discontinuation of soy formula was followed by normalization of the TSH in 3 weeks and helped attain a subsequent decrement of L-thyroxine dose to 8.6 micrograms/kg/day. Neither the hyperthyroxinemia nor hyperthyrotropinemia in these infants was associated with any adverse behavioral-developmental consequence.
When initiating soy-formula feeding in infants with congenital hypothyroidism, the L-thyroxine dose should be increased because of significant reduction in intestinal absorption: conversely, when soy feeding is discontinued, the L-thyroxine dose should be decreased.
Energy balances were measured by indirect calorimetry in four experiments on male growing rats, fed restrictively on isoenergetic and isonitrogenous (10% CP) diets based on either casein supplemented with methionine, or soy protein isolate (experiments 1, 2 and 3) and soy protein isolate supplemented with methionine (experiment 0), respectively. At the end of experiments the rats were killed for body analysis and determination of thyroid hormones and lipids in blood as well as mitochondrial respiration in liver and heart. Feeding of non-supplemented soy protein resulted in a lower efficiency of energy utilisation as well as a lower protein utilisation compared to casein-fed and supplemented soy protein-fed rats. Chemical body composition was not markedly different between the dietary groups. After long-term feeding of soy protein (experiment 3) mass and mitochondrial protein content of the interscapular brown adipose tissue were increased compared to casein-fed rats. Serum thyroid hormone levels were not changed (T3 and free T3) or were significantly lowered (T4 and free T4) following soy protein feeding in comparison with casein feeding (except for experiment 2). Cholesterol and triglycerides were decreased on an average in response to soy protein or supplemented soy protein feeding. In two of three experiments a significant lower efficiency of hepatic mitochondrial respiration with succinate as substrate, expressed by the ratio of added ADP to oxygen consumed, was observed in soy protein-fed rats compared to casein-fed rats.
Genistein, a natural isoflavone phytoestrogen present in soybeans, caused a dose-dependent growth inhibition of the two hormone-sensitive cell lines T47D and ZR75.1 and of the two hormone-independent cell lines MDAMB-231 and BT20. Flow cytometric analysis of cells treated for 4 days with 15 and 30 microM genistein showed a dose-dependent accumulation in the G(2)M phase of the cell cycle. At the highest tested concentration, there was a sevenfold increase in the percentage of cells in G(2)M (63%) with respect to the control (9%) in the case of T47D cells and a 2.4-fold increase in the case of BT20. An intermediate fourfold accumulation was observed in the case of MDAMB-231 and ZR75.1. The G(2)M arrest was coupled with a parallel depletion of the G(0)/G(1) phase. To understand the mechanism of action underlying the block in G(2)M induced by genistein, we investigated the expression and the activity of cyclins and of cyclin-dependent kinases specifically involved in the G(2)-->M transition. As expected, p34(cdc-2) expression, monitored by Western blotting, was unaffected by genistein treatment in all cell lines. With exception of the T47D cell line, we revealed an increase in the tyrosine phosphorylated form of p34, suggesting an inactivation of the p34(cdc-2) catalytic activity consequent to treatment of cells with genistein. In fact, immunoprecipitates from genistein-treated MDAMB-231 and BT20 cells displayed a fourfold decrease in kinase activity evaluated using the histone H1 as substrate. Conversely, no variation in kinase activity was observed between treated and untreated ZR75.1 cells despite the increase in p34 phosphorylation. In cells treated with 30 microM genistein, cyclin B(1) (p62) increased 2.8-,8-and 103-fold, respectively, in BT20, MDAMB-231, and ZR75.1 cells, suggesting an accumulation of the p62, which is instead rapidly degraded in cycling cells. No effects were observed on cyclin expression in T47D cells. We therefore conclude that genistein causes a G(2)M arrest in breast cancer cell lines, but that such growth arrest is not necessarily coupled with deregulation of the p34(cdc-2)/cyclin B(1) complex only in all of the studied cell lines.
Phytoestrogens are a chemically diverse group of compounds made by plants that can have estrogenic effects in animals. Both tumorigenic and antitumorigenic effects have been reported. Although estrogens stimulate the growth of many breast tumors, there is a negative correlation between the incidence of breast cancer and the phytoestrogen-rich diet of certain Asian populations. To begin to resolve this paradox, we have analyzed the estrogenic properties of genistein and quercetin, two flavonoid phytoestrogens particularly abundant in soybeans. Trans-activation experiments with a transfected reporter gene for nuclear estrogen receptors (ER) show strong activation of the endogenous ER alpha by both phytoestrogens in two MCF7 human breast cancer cell lines. This is supported by the observation that the two phytoestrogens induce the down-regulation of ER alpha mRNA and protein levels. Using chimeric proteins consisting of the hormone binding domains of ER alpha and ER beta fused to the Gal4 DNA binding domain, we have established that genistein and quercetin are full estrogenic agonists of both ER isoforms. Ligand binding experiments with purified ER alpha and ER beta confirm that the two phytoestrogens are ER ligands. At concentrations that are sufficient to obtain substantial transcriptional activity, they stimulate the proliferation of two ER alpha-dependent breast cancer cell lines. At high concentrations, such as those reached with a soy-rich diet, genistein and quercetin are strong cytotoxic agents that even kill ER-independent HeLa cells. Thus, the mode of action of phytoestrogens and the balance between being risk or chemopreventive factors for breast cancer may depend on the dietary load.
Autoimmunity to thyroid antigens leads to two distinct pathogenic processes with opposing clinical outcomes: hypothyroidism in Hashimoto's thyroiditis and hyperthyroidism in Graves' disease. The high frequency of these diseases and easy accessibility of the thyroid gland has allowed the identification of key pathogenic mechanisms in organ-specific autoimmune diseases. In early investigations, antibody- and T-cell-mediated death mechanisms were proposed as being responsible for autoimmune thyrocyte depletion. Later, studies on apoptosis have provided new insights into autoimmune target destruction, indicating the involvement of death receptors and cytokine-regulated apoptotic pathways in the pathogenesis of thyroid autoimmunity.
To test the hypothesis that feeding soy formula to infants with congenital hypothyroidism (CH) leads to prolonged increase of thyroid stimulating hormone (TSH).
The study was a review of 78 patients seen during their first year of life between 1990 and 1998. Data regarding clinical diagnosis, date of treatment initiation, TSH, levothyroxine dose, weight, length, and diet information from each visit were collected from the charts.
There were eight patients in the soy diet group and 70 in the non-soy diet group. There was no significant difference between the two groups in the starting dose of levothyroxine or the change in this dose over one year. There was a significant difference between the two groups in the following areas: time to TSH normalisation, first TSH on treatment, percentage with increased TSH at 4 months of age, percentage with increased TSH throughout the first year of life, and in the overall trend of TSH at each visit.
Infants fed soy formula had prolonged increase of TSH when compared to infants fed non-soy formula. These infants need close monitoring of free thyroxine and TSH measurements, and they may need increased levothyroxine doses to achieve normal thyroid function tests.
Autoantibodies against human thyroglobulin are a hallmark of autoimmune thyroid disease in humans, and are often found in normal subjects. Their pathogenic significance is debated. Several B-cell epitope-bearing peptides have been identified in thyroglobulin. They are generally located away from the cysteine-rich regions of tandem sequence repetition. It is possible that our current epitopic map is incomplete because of the difficulty that proteolytic and recombinant approaches have in restituting conformational epitopes based upon proper pairing between numerous cysteinyl residues. Furthermore, the homology of cysteine-rich repeats with a motif occurring in several proteins, endowed with antiprotease activity, suggests that these regions may normally escape processing and presentation to the immune system, and brings attention to the mechanisms, such as oxidative cleavage, by which such cryptic epitopes may be exposed. A number of T-cell epitope-bearing peptides, endowed with thyroiditogenic power in susceptible mice, were also identified. None of them was dominant, as none was able to prime in vivo lymph node cells that would proliferate or transfer autoimmune thyroiditis to syngeneic hosts, upon stimulation with intact thyroglobulin in vitro. More than half of them are located within the acetylcholinesterase-homologous domain of thyroglobulin, and overlap B-cell epitopes associated with autoimmune thyroid disease, while the others are located within cysteine-rich repeats. The immunopathogenic, non-dominant character of these epitopes also favours the view that the development of autoimmune thyroid disease may involve the unmasking of cryptic epitopes, whose exposure may cause the breaking of peripheral tolerance to thyroglobulin. Further research in this direction seems warranted.
Thyroglobulin (Tg) is cleaved into several peptides during thyroid hormone synthesis, an oxidative process. P40, an iodinated C-terminal peptide from human Tg, has a molecular weight of about 40 kDa and contains two hormonogenic sites. P40 is the smallest peptide that is still recognized by monoclonal antibodies from mice immunized with human Tg directed against its immunodominant region. Since P40 also contains several T-cell epitopes, it is a good candidate for studying the primary events involved in the process of hormone synthesis leading to thyroid autoimmunity. The present results show that P40 is recognized by Tg antibodies from patients with thyroid disorders and induces Tg antibodies in CBA mice. P40 may therefore be involved in the autoimmune process, thus providing a useful tool for diagnostic and therapeutic purposes.
Phytoestrogens have the potential to maintain bone health and delay or prevent osteoporosis. This review focuses on their dose-dependent effects on bone and their possible mechanisms of action. Phytoestrogens exert biphasic dose-dependent effects on osteoblasts and osteoprogenitor cells, stimulating osteogenesis at low concentrations and inhibiting osteogenesis at high concentrations. They inhibit osteoclast formation and activity. Recent data show that the balance between estrogen receptors and peroxisome proliferator-activated receptors, which are dose-dependently activated by phytoestrogens, determines their biological effects on bone. This review provides a new understanding of the mechanism of action of phytoestrogens and could be important for future studies to find precise beneficial doses in vivo and in clinical trials.
Thyroid hormones and thyroid autoantibodies, along with serum concentrations of two phytoestrogens of the isoflavone series, daidzein and genistein, were measured in 268 children without overt thyroid diseases, screened for iodine deficiency in one region of the Czech Republic. Since both phytoestrogens have been reported to inhibit thyroid hormone biosynthesis and in high concentrations to exert goitrogenic effects, we investigated whether their presence in the circulation could influence thyroid hormone function in a population where soy consumption is not common. Correlation analysis revealed a significant positive association of genistein with thyroglobulin autoantibodies and a negative correlation with thyroid volume. Multiple regression analysis of the relationships between actual phytoestrogen levels and measured thyroid parameters revealed only a weak but significant association between genistein and thyroid variables. Higher levels of free thyroxine were found in a subgroup of 36 children who ate soy food in the previous 24 h. In conclusion, only modest association was found between actual phytoestrogen levels and parameters of thyroid function. On the other hand, even small differences in soy phytoestrogen intake may influence thyroid function, which could be important when iodine intake is insufficient.
Soy foods are a traditional staple of Asian diets but because of their purported health benefits they have become popular in recent years among non-Asians, especially postmenopausal women. There are many bioactive soybean components that may contribute to the hypothesized health benefits of soy but most attention has focused on the isoflavones, which have both hormonal and nonhormonal properties. However, despite the possible benefits concerns have been expressed that soy may be contraindicated for some subsets of the population. One concern is that soy may adversely affect thyroid function and interfere with the absorption of synthetic thyroid hormone. Thus, the purpose of this review is to evaluate the relevant literature and provide the clinician guidance for advising their patients about the effects of soy on thyroid function. In total, 14 trials (thyroid function was not the primary health outcome in any trial) were identified in which the effects of soy foods or isoflavones on at least one measure of thyroid function was assessed in presumably healthy subjects; eight involved women only, four involved men, and two both men and women. With only one exception, either no effects or only very modest changes were noted in these trials. Thus, collectively the findings provide little evidence that in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function. In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients. However, hypothyroid adults need not avoid soy foods. In addition, there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate.
The ability of soy isoflavones to inhibit thyroid peroxidase and induce goiter in animals has generated concern regarding their potential antithyroid effects in humans. The purpose of this study was to determine the effects of soy protein isolates of varied isoflavone content on circulating thyroid hormones in healthy young men.
Thirty-five healthy men (27.9 +/- 5.7 years old) supplemented their habitual diets with milk protein isolate (MPI), low-isoflavone soy protein isolate (low-iso SPI; 1.64 +/- 0.19 mg iso/day), and high-isoflavone SPI (high-iso SPI; 61.7 +/- 7.4 mg iso/day) for 57 days each, separated by 4-week washouts in a randomized crossover design. Blood was collected on days 1, 29, and 57 of each treatment for analysis of total triiodothyronine (T3), free T3, total thyroxine (T4), free T4, thyroid stimulating hormone (TSH), and thyroid binding globulin (TBG). Twenty-four hour urines were collected at the end of each treatment for analysis of isoflavones.
Results revealed no significant effects of the low-iso or high-iso SPIs on serum total T3, free T3, total T4, free T4, TSH, or TBG when compared with the MPI on either study days 29 or 57. Urinary data revealed that isoflavones were significantly increased by the high-iso SPI relative to the low-iso SPI and MPI.
Results of this study demonstrate that soy isoflavones in a protein matrix do not significantly influence circulating thyroid hormones in healthy young men.
The human mast cell line (HMC-1(560)) was used to study the effects of tyrosine kinase (TyrK) inhibition on histamine release in consequence of intracellular Ca2+ or pH changes. This is important since the TyrK inhibitor STI571 (Glivec) inhibits proliferation and induces apoptosis in HMC-1(560). HMC-1(560) cells have a mutation in c-kit, which leads to a permanent phosphorylation of the KIT protein and their ligand-independent proliferation. The TyrK inhibitors STI571, lavendustin A and genistein decrease spontaneous histamine release in 24-h pre-incubated cells. Results are compared with those of the mast cell stabiliser cromoglycic acid, which also drops spontaneous histamine release. When exocytosis is stimulated by alkalinisation, STI571 pre-incubated cells release more histamine than non-pre-incubated cells. Alkalinisation-induced histamine release reaches still higher levels in STI571 cells with activated protein kinase C (PKC) by PMA. We do not observe modifications on histamine release in cells, treated with PKC inhibitors (rottlerin, Gf109203 or Gö6976). Lavendustin A- and genistein 24-h incubated cells behave similar to STI571 cells, whereas cromoglycic acid does not show effects after stimulation with alkalinisation. Stimulation of exocytosis with the Ca2+ ionophore ionomycin does not modify histamine response in TyrK inhibited cells. Ca2+ and pH changes are observed after long-time incubation with STI571. Results show that pH is still higher in STI571 pre-incubated cells after alkalinisation with NH4Cl, whereas intracellular Ca2+ concentration remains stable. This work further strength the importance of pHi as a cell signal and suggest that STI571 has transduction pathways in common with other TyrKs.
There is growing evidence that, in addition to the reproductive system, the hypothalamic-pituitary-thyroid axis is a target of endocrine-disrupting compounds (EDCs). However, this is not reflected adequately in current screening and assessment procedures for endocrine activity that to date determine only general parameters of thyroid function.
We used several in vitro and ex vivo assays in an attempt to identify suitable biomarkers for antithyroid action testing a selected panel of putative EDCs.
In vitro we detected stimulation or inhibition of iodide uptake into FRTL-5 rat thyroid cells, inhibition of thyroid hormone binding to transthyretin, agonistic or antagonistic effects in a thyroid hormone receptor-dependent reporter assay, and inhibition of thyroid peroxidase using a novel assay system based on human recombinant thyroperoxidase that might be suitable for routine screening for potential EDCs. In rats, chronic application of several EDCs led to changes in thyroid morphology, alterations of thyrotropin and thyroid hormone serum levels as well as alterations in peripheral thyroid hormone-regulated end points such as malic enzyme and type I 5'-deiodinase activity.
As the effects of EDCs do not reflect classic mechanisms of hormone-dependent regulation and feedback, we believe multitarget and multimodal actions of EDCs affect the hypothalamic-pituitary-thyroid axis. These complex effects require a diverse approach for screening, evaluation, and risk assessment of potential antithyroid compounds. This approach involves novel in vitro or cell-based screening assays in order to assess thyroid hormone synthesis, transport, metabolism, and action as well as in vivo assays to measure thyroid hormone-regulated tissue-specific and developmental end points in animals.
Epidemiological investigations suggest that soy consumption may be associated with a lower incidence of certain chronic diseases. Clinical studies also show that ingestion of soy proteins reduces the risk factors for cardiovascular disease. This led to the approval of the food-labeling health claim for soy proteins in the prevention of coronary heart disease by the U.S. FDA in 1999. Similar health petitions for soy proteins have also been approved thereafter in the United Kingdom, Brazil, South Africa, the Philippines, Indonesia, Korea, and Malaysia. However, the purported health benefits are quite variable in different studies. The Nutrition Committee of the American Heart Association has assessed 22 randomized trials conducted since 1999 and found that isolated soy protein with isoflavones (ISF) slightly decreased LDL cholesterol but had no effect on HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure. The other effects of soy consumption were not evident. Although the contributing factors to these discrepancies are not fully understood, the source of soybeans and processing procedures of the protein or ISF are believed to be important because of their effects on the content and intactness of certain bioactive protein subunits. Some studies have documented potential safety concerns on increased consumption of soy products. Impacts of soy products on thyroid and reproductive functions as well as on certain types of carcinogenesis require further study in this context. Overall, existing data are inconsistent or inadequate in supporting most of the suggested health benefits of consuming soy protein or ISF.
Autoimmune thyroiditis, also known as chronic lymphocytic or Hashimoto's thyroiditis, is characterized by infiltration of the thyroid gland by inflammatory cells and production of autoantibodies to thyroid-specific antigens thyroglobulin and thyroperoxidase. It is accompanied by hypothyroidism due to destruction and eventual fibrous replacement of the follicle cells. Autoimmune thyroiditis is clearly multifactorial in etiology with genetic and environmental factors contributions. Excess dietary Iodine can exacerbate thyroiditis in genetically susceptible hosts such as the NOD.H2(h4) mouse. In this mouse excess dietary iodine leads to an increased immunogenicity of the thyroglobulin molecule and enhanced expression of ICAM-1 on thyroidal follicle cells. We present evidence here that ICAM-1 expression is enhanced by the elevated generation of reactive oxygen species (ROS). The anti-oxidant diphenyleneiodium (DPI), an inhibitor of NADPH oxidase, reduced both the generation of ROS and of ICAM-1 expression in cultures of NOD.H2(h4) mouse thyrocytes. These results suggest that antioxidants may have therapeutic value in preventing autoimmune thyroiditis.
- Wilgus HS
- Sharpless GR