Disruption of Thyroid Hormone Function by Environmental Pollutants

Abstract

A great number of synthetic chemicals are released into the environment, many of which are known or thought to interfere with normal thyroid hormone (TH) function. THs play important roles in regulating growth and development and maintaining metabolic homeostasis. For example, amphibian tadpole metamorphosis is a TH-triggered and controlled developmental process, and has proven to be useful as a screening tool for environmental pollutants suspected of disrupting TH functions. TH disruption is thought to be caused through a variety of mechanisms, including increased thyroxine (T 4 ) metabolism by uridine diphosphate glucuronyl transferases (UDPGTs), blocking TH signaling through TH receptors (TRs), and induction of mitochondrial membrane permeability transition (MPT). As our knowledge concerning the specific effects of these chemicals is very limited, further research is needed to obtain accurate information to be used in establishing guidelines for the protection of health in humans and wildlife.

Polyhalogenated aromatic hydrocarbons and metabolites: Relation to circulating thyroid hormone and retinol in nestling bald eagles (Haliaeetus leucocephalus)

“…In particular, many of these compounds have been shown to compromise thyroid function, specifically altering normal synthesis, secretion, transport, metabolism, binding, and excretion of thyroid hormones [1,2,19,20]. Thyroid hormones are essential for normal growth and development; any disruption in their levels could have significant consequences especially for developing young [3,19,21,22].…”

Thyroid signaling in immune organs and cells of the teleost fish rainbow trout (Oncorhynchus mykiss)

“…But, in addition, such information is significant with regard to potential impacts of thyroid-disrupting chemicals present in the environment (reviewed in Refs. [8,32,34]) to which natural fish populations and aquaculture facilities may be exposed [55].…”

Environmental factors affecting thyroid function of wild sea bass (Dicentrarchus labrax) from European coasts

“…Serum half-life of thyroxin (T 4 ) is controlled in part by serum binding proteins like ThyroxinBinding-Globulin (TBG), Transthyretin (TTR) and albumin. PCBs and related compounds are structurally similar to thyroid hormones and are well known to displace T 4 from serum binding proteins (Lans et al, 1994;Brouwer et al, 1998;Brucker-Davis, 1998;Funkenstein et al, 2000;Marino and McCluskey, 2000;Ishihara et al, 2003;Boas et al, 2006;Kashiwagi et al, 2009). This may cause a decline in serum thyroid hormone concentration by biliary clearance, inducing a release of TSH provoking the observed increase of synthesis and secretion activity of the gland.…”