Impacto da exposição materna ao triclosan durante a gestação sobre a atividade do eixo hipotálamo-hipófise-tireoide da prole
Data
2023-04-14
Autores
Henrique, Guilherme 
Orientadores
Serrano-Nascimento, Caroline
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Introdução: O triclosan (TCS) é um composto antimicrobiano lipofílico amplamente
utilizado na produção de produtos de cuidado pessoal e doméstico. A exposição ao
TCS foi previamente associada à redução dos níveis séricos de hormônios
tireoidianos (HT) e distúrbios na glândula tireoide. No entanto, os efeitos da exposição
ao TCS na programação de disfunções tireoidianas não foram estudados. Objetivos:
Investigar o impacto da exposição intrauterina ao TCS sobre a tireoide dos animais
das proles durante diferentes períodos de desenvolvimento. Métodos: Ratas Wistar
prenhes foram tratadas oralmente com óleo de milho (controle) ou óleo de milho
suplementado com TCS (10 ou 30 mg/kg/dia) durante toda a gestação. Os machos e
fêmeas das proles foram eutanasiados no dia gestacional 20 (GD20) ou no 90º dia
pós-natal (PND90). A expressão gênica/proteica do hipotálamo, hipófise, tireoide e
fígado foi avaliada por RT-qPCR e Western Blotting. A morfologia da tireoide foi
analisada por histologia. A metilação global do DNA da tireoide, os níveis de HT e do
hormônio tireoestimulante (TSH) foram mensurados por ensaios ELISA,
quimioluminescência e fluorometria, respectivamente. Resultados: A exposição
intrauterina ao TCS aumentou a expressão de genes envolvidos na síntese de HT e
o conteúdo de tireoperoxidase (TPO) na tireoide dos machos e fêmeas das proles em
GD20. Interessantemente, a expressão gênica/proteica do co-transportador sódioiodeto
(NIS) foi reduzida em animais expostos ao TCS. A expressão das enzimas
envolvidas no controle epigenético da expressão gênica foi alterada na tireoide de
animais tratados com TCS. O conteúdo das histonas H3 e H4 acetiladas (H3Ac e
H4Ac) apresentou-se reduzido em animais expostos ao TCS durante o período
intrauterino. Em PND90, a exposição intrauterina ao TCS alterou a expressão do
hormônio liberador de tireotrofina (TRH) no hipotálamo, a expressão da subunidade
beta do TSH (TSHB) na hipófise e os níveis séricos de TSH em nos machos e fêmeas
adultos das proles. Além disso, a exposição intrauterina ao TCS diminuiu a expressão
de genes e proteínas envolvidos na síntese de HT na tireoide. Esses dados foram
consistentes com a redução nos níveis séricos de tiroxina (T4) em machos e fêmeas
das proles. Finalmente, os animais expostos ao TCS apresentaram folículos
tireoidianos deformados, destruição das células foliculares tireoidianas e intensa
infiltração inflamatória em ambas as doses estudadas. Em ambos os sexos, a
exposição intrauterina ao TCS aumentou a metilação global do DNA na tireoide,
diminuiu o conteúdo de histonas H3 e H4 acetiladas, bem como aumentou o conteúdo
de histona H3 trimetilada nas lisinas 9 e 27. Além disso, a exposição ao TCS alterou
a expressão de enzimas hepáticas envolvidas no metabolismo periférico de HT.
Conclusões: A exposição intrauterina ao TCS durante um período crítico de
desenvolvimento desregulou a estrutura, expressão gênica e função da tireoide ao
nascimento e durante a idade adulta dos animais das proles. Mecanismos
epigenéticos parecem estar envolvidos na ativação (em GD20) ou repressão (em
PND90) da transcrição gênica em animais expostos ao TCS. A exposição intrauterina
ao TCS programou a tireoide e aumentou a suscetibilidade dos indivíduos das proles
de desenvolver hipofunção da tireoide durante a idade adulta.
Introduction: Triclosan (TCS) is a lipophilic antimicrobial compound widely used in personal and household care products. TCS exposure has been previously associated with reduced thyroid hormone (TH) serum levels and thyroid disorders. Nevertheless, the effects of TCS exposure in the programming of thyroid dysfunctions have not been studied. Objectives: To investigate the impact of intrauterine exposure to TCS in the thyroid of offspring rats during different periods of development. Methods: Pregnant Wistar rats were orally treated with corn oil (control) or corn oil supplemented with TCS (10 or 30 mg/kg/day) throughout the gestation. The male and female offspring rats were euthanized at gestational day 20 (GD20) and the 90th postnatal day (PND90). Hypothalamus, pituitary, thyroid, and liver gene/protein expression was evaluated by RT-qPCR and Western Blotting. Thyroid histological analysis was performed. Thyroid DNA global methylation, TH and thyroid-stimulating hormone (TSH) levels were measured by ELISA, chemiluminescence, and fluorometric assays, respectively. Results: Intrauterine exposure to TCS increased the mRNA expression of genes involved in TH synthesis and the thyroperoxidase (TPO) content in the thyroid of GD20 offspring rats. Interestingly, sodium/iodide symporter (NIS) gene and protein expression were reduced in TCS-exposed animals. The expression of enzymes involved in the epigenetic control of gene expression was altered in the thyroid of TCS treated animals. The acetylated histones H3 and H4 (H3Ac and H4Ac) content was reduced in the animals exposed to TCS during the intrauterine period. At PND90, the intrauterine exposure to TCS altered the thyrotropin-releasing hormone (TRH) expression in the hypothalamus, the TSH subunit beta (TSHB) expression in the pituitary, and the TSH serum levels in adult male and female offspring animals. In addition, intrauterine exposure to TCS decreased the thyroid expression of genes and proteins involved in TH synthesis. Consistently, there was a reduction in the serum levels of thyroxine (T4) in males of the offspring at both doses and in the females exposed to the lowest TCS dose. Finally, TCS-exposed animals presented misshapen thyroid follicles, thyroid follicular cell destruction, and intense inflammatory infiltration in both studied doses. In both sexes, intrauterine exposure to TCS increased the thyroid DNA global methylation, decreased the content of acetylated histones H3 and H4, and increased the content of histone H3 trimethylated at the lysine 9 and 27. Moreover, TCS exposure altered the expression of hepatic enzymes involved in TH peripheral metabolism. Conclusions: Intrauterine exposure to TCS during a critical development period disrupted the thyroid gland structure, gene expression, and function at birth and adulthood. Specific epigenetic mechanisms seem to be involved in the activation (at GD20) or repression (at PND90) of gene transcription in TCS exposed animals. Intrauterine exposure to TCS has programmed the thyroid and increased the susceptibility of offspring rats to develop thyroid hypofunction during adulthood.
Introduction: Triclosan (TCS) is a lipophilic antimicrobial compound widely used in personal and household care products. TCS exposure has been previously associated with reduced thyroid hormone (TH) serum levels and thyroid disorders. Nevertheless, the effects of TCS exposure in the programming of thyroid dysfunctions have not been studied. Objectives: To investigate the impact of intrauterine exposure to TCS in the thyroid of offspring rats during different periods of development. Methods: Pregnant Wistar rats were orally treated with corn oil (control) or corn oil supplemented with TCS (10 or 30 mg/kg/day) throughout the gestation. The male and female offspring rats were euthanized at gestational day 20 (GD20) and the 90th postnatal day (PND90). Hypothalamus, pituitary, thyroid, and liver gene/protein expression was evaluated by RT-qPCR and Western Blotting. Thyroid histological analysis was performed. Thyroid DNA global methylation, TH and thyroid-stimulating hormone (TSH) levels were measured by ELISA, chemiluminescence, and fluorometric assays, respectively. Results: Intrauterine exposure to TCS increased the mRNA expression of genes involved in TH synthesis and the thyroperoxidase (TPO) content in the thyroid of GD20 offspring rats. Interestingly, sodium/iodide symporter (NIS) gene and protein expression were reduced in TCS-exposed animals. The expression of enzymes involved in the epigenetic control of gene expression was altered in the thyroid of TCS treated animals. The acetylated histones H3 and H4 (H3Ac and H4Ac) content was reduced in the animals exposed to TCS during the intrauterine period. At PND90, the intrauterine exposure to TCS altered the thyrotropin-releasing hormone (TRH) expression in the hypothalamus, the TSH subunit beta (TSHB) expression in the pituitary, and the TSH serum levels in adult male and female offspring animals. In addition, intrauterine exposure to TCS decreased the thyroid expression of genes and proteins involved in TH synthesis. Consistently, there was a reduction in the serum levels of thyroxine (T4) in males of the offspring at both doses and in the females exposed to the lowest TCS dose. Finally, TCS-exposed animals presented misshapen thyroid follicles, thyroid follicular cell destruction, and intense inflammatory infiltration in both studied doses. In both sexes, intrauterine exposure to TCS increased the thyroid DNA global methylation, decreased the content of acetylated histones H3 and H4, and increased the content of histone H3 trimethylated at the lysine 9 and 27. Moreover, TCS exposure altered the expression of hepatic enzymes involved in TH peripheral metabolism. Conclusions: Intrauterine exposure to TCS during a critical development period disrupted the thyroid gland structure, gene expression, and function at birth and adulthood. Specific epigenetic mechanisms seem to be involved in the activation (at GD20) or repression (at PND90) of gene transcription in TCS exposed animals. Intrauterine exposure to TCS has programmed the thyroid and increased the susceptibility of offspring rats to develop thyroid hypofunction during adulthood.