Contaminant effects on the teleost fish thyroid

Abstract

Abstract-Numerous environmentally relevant chemicals, including polychlorinated hydrocarbons, polycyclic aromatic hydrocarbons, organochlorine pesticides, chlorinated paraffins, organophosphorous pesticides, carbamate pesticides, cyanide compounds, methyl bromide, phenols, ammonia, metals, acid loads, sex steroids, and pharmaceuticals, exert acute or chronic effects on the thyroid cascade in the approximately 40 teleost fish species tested to date. Thyroid endpoints, therefore, serve as biomarkers of exposure to environmental pollutants. However, the mechanisms underlying thyroid changes and their physiological consequences are poorly understood because the thyroid cascade may respond indirectly and it has considerable capacity to compensate for abuses that otherwise would disrupt thyroid hormone homeostasis. Indeed, a xenobiotic-induced change in fish thyroid function has yet to be conclusively causally linked to decreased fitness or survival. Other complications in interpretation arise from the diversity of test conditions employed and the often indiscriminate use of numerous thyroid endpoints. Future work should be directed toward standardizing test conditions and thyroid endpoints and investigating causal links between thyroid changes and fish growth, reproduction, and development. Development may be particularly susceptible to thyroid disruption, and thyroid endpoints appropriate for early life stages need to be applied.

Waterborne exposure to PFOS causes disruption of the hypothalamus–pituitary–thyroid axis in zebrafish larvae

“…Deiodinase activity is critical for regulation of tissue TH concentrations and is strongly affected by serum TH concentrations (Mol et al, 1999;Orozco and Valverde, 2005). Previous studies have shown that deiodinase activity in fish is sensitive to environmental contaminants, such as metals, polychlorinated biphenyls and pesticides (Cyr et al, 1988;Brown et al, 2004;Coimbra et al, 2005;Li et al, 2009), and they have recommended including a measure of deiodination gene expressions as sensitive biomarkers of thyroid disruption in fish upon exposure to environmental chemicals (Picard-Aitken et al, 2007;Li et al, 2009). In the present study, we found a significant increase in Dio1 gene expression, but no significant effects on Dio2 gene expression.…”

Environmental contaminants and biomarker responses in fish from the Rio Grande and its U.S. tributaries: Spatial and temporal trends

“…Similar observations were made for carp from some sites in the lower MRB sampled in 1995 (Blazer et al, 2002). Thyroid hyperplasia in fish and other organisms has been induced by exposure to a wide array of contaminants (e.g., Patiño et al, 2003 and studies cited by Blazer et al, 2002) and, along with endpoints indicative of thyroid function and homeostasis (see review by Brown et al, 2004), may represent a potential biomarker for contaminant effects on thyroid function. However, the effects of confounding factors such as area of kidney sampled and fish age on thyroid histopathology need to be evaluated.…”

Assessing reproductive and endocrine parameters in male largescale suckers (Catostomus macrocheilus) along a contaminant gradient in the lower Columbia River, USA

“…Three PCB congeners were negatively correlated with T4, yet both T4 and T3 were positively correlated with pentachloroanisole and dieldrin (Table 6). Some studies have shown PCBs and certain pesticides may alter 5′-deiodinase activity in fish, leading to increased T3 and reduced T4 (Brar et al 2010;Brown et al 2004). As previously suggested, plasma levels of T4 and T3 may be inconsistent biomarkers of thyroid disruption in teleosts (Carr and Patiño, 2011).…”

“…Measures of thyrocyte height, an index of hypertrophy, did not yield statistical site differences, but values were smallest at LV (Table 4). Although the thyroid endocrine system plays a role in gonadal development and reproduction of teleosts (Cyr and Eales, 1996), the effects of thyroid endocrine disruption on reproductive fitness have been difficult to document (Brown et al, 2004;Carr and Patiño, 2011). Recent studies with zebrafish have indicated a relationship between the status of the thyroid endocrine system and gonadal sex differentiation, pubertal development, and reproduction Sharma and Patiño, 2013).…”