Induction of Thyroid Hormones Disruption by Exposure of Dioxins and Phthalates: A Comprehensive Review

Abstract

The main objective of this study is to elaborate the crucial effect of dioxins and phthalates on thyroid hormones such as tetraiodothyronine (T4) and tri-iodothyronine (T3) in body fluids. The literature evidences have been collected from Google Scholar, PubMed and Medline by using different key words. All literature evidences showed a drastic effect of dioxins and phthalates on the status of thyroid hormones. Hexachlorobenzene (HCB) is an environmental pollutant that increases activity of malic enzyme (ME) by increasing ME gene transcription. ME interact with aryl hydrocarbon receptors (AhR) and modulate the expression of genes with specific xenobiotic or DRE in their promoters that respond to dioxin. HCB increases activity of thyroid enzymes whose induction depends on thyroid hormone (TH) levels. Dioxin decreases T4 levels and increases TSH levels in neonatal plasma. Dioxin and HCB also causes various disorders in infants. Phthalates disrupt the thyroid hormones levels especially in pregnant women and infants through various mechanisms. Phthalates mainly decrease T4 levels and further studies are in process to describe exact mechanism.