Assuntos

RESUMO

Thyroid hormones (THs) are required for the growth and development of the fetus, stimulating anabolism, and oxygen consumption from the early stages of pregnancy to the period of fetal differentiation close to delivery. Maternal changes in the hypothalamic-pituitary-thyroid axis are also well known. In contrast, several open questions remain regarding the relationships between the placenta and the maternal and fetal TH systems. The exact mechanism by which the placenta participates in regulating the TH concentration in the fetus and mother and the role of TH in the placenta are still poorly studied. In this review, we aim to summarize the available data in the area and highlight significant gaps in our understanding of the ontogeny and cell-specific localization of TH transporters, TH receptors, and TH metabolic enzymes in the placenta in both human and rodent models. Significant deficiencies also exist in the knowledge of the contribution of genomic and nongenomic effects of TH on the placenta and finally, how the placenta reacts during pregnancy when the mother has thyroid disease. By addressing these key knowledge gaps, improved pregnancy outcomes and management of women with thyroid alterations may be possible.

Assuntos

RESUMO

Hepatocellular carcinoma (HCC) is the most common primary liver tumor. Hexachlorobenzene (HCB) is an endocrine disruptor and a liver tumor promoter. Deregulation of thyroid hormone (TH) homeostasis may play a significant role in early neoplastic transformation. The aim of this study was to evaluate the relation between TH metabolism and the regulation of cell growth in an in vivo and in vitro model. We examined the role of transforming growth factor-ß1 (TGF-ß1) on TH deiodinase expression and hepatocyte proliferation. An initiation (DEN)/promotion (HCB) tumor model from rat liver and HepG2 cells were used. We evaluated PCNA, p21, p27, SMAD2/3, TGF-ß1, deiodinase 1 (D1), D3, protein expression levels; D1 and D3 mRNA expression; TH and TGF-ß1, D1, D3, and GST-P protein levels in focal/non-focal areas. In vivo, HCB decreased triiodothyronine (T3) and D1 mRNA levels and increased thyroxine (T4) and D3 mRNA levels in liver from DEN+HCB vs. DEN group. HCB increased protein levels from D3, TGF-ß1, and PCNA and decreased D1 in focal-areas. In vitro, HCB increased PCNA, pSMAD 2/3, and TGF-ß1 protein levels and mRNA expression and decreased p21 and p27 protein levels. Exogenous T3 treatment prevent HCB induced molecular alterations related to hepatocyte proliferation whereas T4 did not have any effect. These effects were prevented by using a TGF-ß1 receptor II inhibitor. Results suggest that alteration of TH homeostasis, through D1 function, play a key role in hepatocyte proliferation and that TGF-ß1-SMAD pathway is involved in this process confirming their role in early neoplastic transformation in HCC.

El hepatocarcinoma (HCC) es un tumor hepático primario. El hexaclorobenceno (HCB) es un disruptor endocrino y un promotor de tumores hepáticos. La desregulación de la homeostasis de las hormonas tiroideas (HT) puede ser un proceso importante para la transformación neoplásica temprana. Nuestro objetivo fue evaluar la relación entre el metabolismo de las HT y la regulación de la proliferación celular. Se utilizó un modelo tumoral de iniciación (DEN)/promoción (HCB) de hígado de rata (in vivo) (DEN/HCB) y células HepG2 (in vitro). Evaluamos los niveles de PCNA, p21, p27, SMAD2/3, TGF-ß1, D1, D3, ARNm de D1 y D3, HT y los niveles de TGF-ß1, D1, D3 y GST-P en áreas focales/no focales. In vivo, HCB disminuyó los niveles de T3 y ARNm de la D1 y aumentó los niveles de T4 y ARNm de D3 del grupo DEN + HCB frente al grupo DEN. El HCB aumentó los niveles de D3, TGF-ß1 y PCNA y disminuyó el D1 en las áreas focales. In vitro, HCB aumentó los niveles de PCNA, pSMAD 2/3 y TGF-ß1 y la expresión de ARNm mientras que disminuyó los niveles de p21 y p27. El tratamiento con T3 exógeno previno las alteraciones moleculares relacionadas con la proliferación hepatocitaria. Estos efectos se evitaron utilizando un inhibidor del receptor II de TGF-ß1. Los resultados sugieren que la alteración de la homeostasis de HT, a través de la D1 y la vía TGF-ß1-SMAD, juega un papel clave en la proliferación celular y en las transformaciones neoplásicas tempranas en el HCC.

Assuntos

RESUMO

Abstract Hepatocellular carcinoma (HCC) is the most common primary liver tumor. Hexachlorobenzene (HCB) is an endocrine disruptor and a liver tumor promoter. Deregulation of thyroid hormone (TH) homeostasis may play a significant role in early neoplastic transformation. The aim of this study was to evaluate the relation between TH metabolism and the regulation of cell growth in an in vivo and in vitro model. We examined the role of transforming growth factor-β1 (TGF-β1) on TH deiodinase expression and hepatocyte proliferation. An initiation (DEN)/promotion (HCB) tumor model from rat liver and HepG2 cells were used. We evaluated PCNA, p21, p27, SMAD2/3, TGF-β1, deiodinase 1 (D1), D3, protein expression levels; D1 and D3 mRNA expression; TH and TGF-β1, D1, D3, and GST-P protein levels in focal/non-focal areas. In vivo, HCB decreased triiodothyronine (T3) and D1 mRNA levels and increased thyroxine (T4) and D3 mRNA levels in liver from DEN+HCB vs. DEN group. HCB increased protein levels from D3, TGF-β1, and PCNA and decreased D1 in focal-areas. In vitro, HCB increased PCNA, pSMAD 2/3, and TGF-β1 protein levels and mRNA expression and decreased p21 and p27 protein levels. Exogenous T3 treatment prevent HCB induced molecular alterations related to hepatocyte proliferation whereas T4 did not have any effect. These effects were prevented by using a TGF-β1 receptor II inhibitor. Results suggest that alteration of TH homeostasis, through D1 function, play a key role in hepatocyte proliferation and that TGF-β1-SMAD pathway is involved in this process confirming their role in early neoplastic transformation in HCC.

Resumen El hepatocarcinoma (HCC) es un tumor hepático primario. El hexaclorobenceno (HCB) es un disruptor endocrino y un promotor de tumores hepáticos. La desregulación de la homeostasis de las hormonas tiroideas (HT) puede ser un proceso importante para la transformación neoplásica temprana. Nuestro objetivo fue evaluar la relación entre el metabolismo de las HT y la regulación de la prolifera ción celular. Se utilizó un modelo tumoral de iniciación (DEN)/promoción (HCB) de hígado de rata (in vivo) (DEN/ HCB) y células HepG2 (in vitro). Evaluamos los niveles de PCNA, p21, p27, SMAD2/3, TGF-β1, D1, D3, ARNm de D1 y D3, HT y los niveles de TGF-β1, D1, D3 y GST-P en áreas focales/no focales. In vivo, HCB disminuyó los niveles de T3 y ARNm de la D1 y aumentó los niveles de T4 y ARNm de D3 del grupo DEN + HCB frente al grupo DEN. El HCB aumentó los niveles de D3, TGF-β1 y PCNA y disminuyó el D1 en las áreas focales. In vitro, HCB aumentó los niveles de PCNA, pSMAD 2/3 y TGF-β1 y la expresión de ARNm mientras que disminuyó los niveles de p21 y p27. El tratamiento con T3 exógeno previno las alteraciones moleculares relacionadas con la proliferación hepatocitaria. Estos efectos se evitaron utilizando un inhibidor del receptor II de TGF-β1. Los resultados sugieren que la alteración de la homeostasis de HT, a través de la D1 y la vía TGF-β1-SMAD, juega un papel clave en la proliferación celular y en las transformaciones neoplásicas tempranas en el HCC.

Assuntos

RESUMO

PURPOSE: The potential benefits of treating subclinical hypothyroidism (SCH) are unclear and still controversial. Thus, we surgically induced SCH in rats and evaluated the effects of thyroxine (T4) replacement on the gene expression levels of deiodinases and thyroid hormone (TH) transporters in different tissues. METHODS: SCH was induced by hemithyroid electrocauterization. The control animals underwent the same surgical procedure but were not subjected to electrocauterization (sham). After 14 days, half of the SCH animals were treated with T4 (SCH + T4). At the end of the experimental protocol, all of the rats were euthanized, serum hormone concentrations were measured, and RNA analyses were performed on different tissues and organs. RESULTS: Consistent with previous studies, we observed increased TSH levels, normal TH levels, and reduced hypothalamic TRH expression in the SCH group. Additionally, Dio2 mRNA expression was downregulated in the hippocampus and pituitary, and Dio1 was upregulated in the kidney and pituitary of the SCH animals. The changes in Dio3 expression were tissue-specific. Concerning TH transporters, Mct10 expression was upregulated in the pituitary, kidney, hypothalamus, and hippocampus, and Mct8 expression was downregulated in the kidney of the SCH group. Crym expression was upregulated in the kidney and pituitary. Notably, T4 replacement significantly attenuated serum TSH levels and reverted Dio1, Dio2, Mct10, and Crym expression in the pituitary, hippocampus, and kidney to levels that were similar to the sham group. Tissue-specific responses were also observed in the liver and hypothalamus. CONCLUSION: Our results indicate that treatment of SCH should be considered before the appearance of clinical symptoms of hypothyroidism.

Assuntos

RESUMO

C3H/HeJ (C3H) mice are deficient of type I deiodinase (D1), an enzyme that activates thyroid hormone (TH), converting thyroxine (T4) to triiodothyronine (T3). Nevertheless, C3H mice present normal serum T3 and a gross euthyroid phenotype. To investigate if a global D1 deficiency interferes in the TH effects on bone, we compared bone growth, bone mass accrual and bone strength of C3H and C57BL/6J (B6) mice under abnormal TH status. Four-week-old female mice of both strains were grouped as Euthyroid, Hypothyroid (pharmacologically-induced), 1xT4 and 10xT4 (hypothyroid animals receiving 1- or 10-fold the physiological dose of T4 /day/16 weeks). Hypothyroidism and TH excess similarly impaired body weight (BW) gain and body growth in both mice strains. In contrast, whereas hypothyroidism only slightly impaired bone mineral density (BMD) accrual in B6 mice, it severely impaired BMD accrual in C3H mice. No differences were observed in serum and bone concentrations of T3 between hypothyroid animals of both strains. Interestingly, treatment with 10xT4 was less deleterious to BMD accrual in C3H than in B6 mice and resulted in less elevated T3 serum levels in B6 than in C3H mice, which is probably explained by the lower D1 activity in C3H mice. In addition, hypothyroidism decreased bone strength only in C3H but not in B6 mice, while TH excess decreased this parameter in both strains. These findings indicate that D1 deficiency contributes to the TH excess-induced differences in bone mass accrual in C3H vs. B6 mice and suggest that deiodinase-unrelated genetic factors might account for the different skeleton responses to hypothyroidism between strains.

RESUMO

PURPOSE: The aim of the study was to evaluate thyroid function profile as a possible factor influencing weight and body composition variation in new users of depot medroxyprogesterone acetate (DMPA). MATERIALS AND METHODS: A prospective, non-randomised, comparative study was conducted at the University of Campinas, Brazil. Women aged 18-40 years with a body mass index (BMI) less than 30 kg/m2, normal oral glucose tolerance test, no known diseases, and using no medication, who opted to use DMPA were paired by age (±1 year) and BMI (±1 kg/m2) with women initiating copper intrauterine device (IUD) use. The main outcome measures were thyroid function profile, weight, and body composition, as measured by dual-energy X-ray absorptiometry. We used repeated measures ANOVA to perform comparisons between times and groups. RESULTS: We evaluated 28 DMPA users and 24 IUD users who completed the 12-month follow-up. We observed that FT4 levels were higher at 12 months (compared to baseline) in the DMPA group (p < .0001) and that FT4/FT3 ratio had increased in both groups. Additionally, at 12 months, total body mass had increased around 2 kg and lean mass increased in the DMPA group compared to the IUD group; there was also an increase in weight, BMI, total body mass, and fat mass when compared to baseline. CONCLUSIONS: No changes in thyroid function occurred that could explain the weight increase observed in DMPA users.

Assuntos

RESUMO

Thyroid hormones (THs) are essential for the regulation of several metabolic processes and the energy consumption of the organism. Their action is exerted primarily through interaction with nuclear receptors controlling the transcription of thyroid hormone-responsive genes. Proper regulation of TH levels in different tissues is extremely important for the equilibrium between normal cellular proliferation and differentiation. The iodothyronine deiodinases types 1, 2 and 3 are key enzymes that perform activation and inactivation of THs, thus controlling TH homeostasis in a cell-specific manner. As THs seem to exert their effects in all hallmarks of the neoplastic process, dysregulation of deiodinases in the tumoral context can be critical to the neoplastic development. Here, we aim at reviewing the deiodinases expression in different neoplasias and exploit the mechanisms by which they play an essential role in human carcinogenesis. TH modulation by deiodinases and other classical pathways may represent important targets with the potential to oppose the neoplastic process.

Assuntos

RESUMO

Mercury seems to exert an inhibitory effect on deiodinases, but there are few studies using Thimerosal (TM) as the mercury source. We aimed to elucidate the effect of TM on thyroid hormones peripheral metabolism. Adult Wistar female rats received 0.25 µg or 250 µg TM/100 g BW, IM, twice a week, for a month. We evaluated serum total T3 and T4, D1 activity using 125I-rT3 as tracer, and D2 activity using 125I-T4 NADPH oxidase activity was measured by Amplex-red/HRP method and mRNA levels by real time PCR. Serum T4 was increased and T3 decreased by the greatest dose of TM. Even though D1 activity in pituitary and kidney was reduced by the highest dose of TM, hepatic D1 activity and D1 mRNA levels remained unchanged. D2 activity was also significantly decreased by the highest dose of TM in all CNS samples tested, except cerebellum, but D2 mRNA was unaltered. mRNA levels of the tested NADPH oxidases were not affected by TM and NADPH oxidase activity was either unaltered or decreased. Our results indicate that TM might directly interact with deiodinases, inhibiting their activity probably by binding to their selenium catalytic site, without changes in enzyme expression.

RESUMO

Thyroid hormones (TH) are critical regulators of several physiological processes, which include development, differentiation and growth in virtually all tissues. In past decades, several studies have shown that changes in TH levels caused by thyroid dysfunction, disruption of deiodinases and/or thyroid hormone receptor (TR) expression in tumor cells, influence cell proliferation, differentiation, survival and invasion in a variety of neoplasms in a cell type-specific manner. The function of THs and TRs in neoplastic cell proliferation involves complex mechanisms that seem to be cell specific, exerting effects via genomic and nongenomic pathways, repressing or stimulating transcription factors, influencing angiogenesis and promoting invasiveness. Taken together, these observations indicate an important role of TH status in the pathogenesis and/or development of human neoplasia. Here, we aim to present an updated and comprehensive picture of the accumulated knowledge and the current understanding of the potential role of TH status on the different hallmarks of the neoplastic process.

Assuntos