Thyroid dysfunction in sea bass (Dicentrarchus labrax): Underlying mechanisms and effects of polychlorinated biphenyls on thyroid hormone physiology and metabolism

Abstract

a b s t r a c tThe current study examines the effect of subchronic exposure to a mixture of Aroclor standards on thyroid hormone physiology and metabolism in juvenile sea bass. The contaminant mixture was formulated to reflect the persistent organic pollution to which the European sea bass population could conceivably be exposed (0.3, 0.6 and 1.0 g 7PCBs per g food pellets) and higher (10 g 7PCBs per g food pellets). After 120 days of exposure, histomorphometry of thyroid tissue, muscular thyroid hormone concentration and activity of enzymes involved in metabolism of thyroid hormones were assessed. Mean concentrations of 8, 86, 142, 214 and 2279 ng g −1 ww ( 7 ICES PCB congeners) were determined after 120 days exposure. The results show that the effects of PCB exposures on the thyroid system are dose-dependent. Exposure to environmentally relevant doses of PCB (0.3-1.0 g 7PCBs per g food pellets) induced a larger variability of the follicle diameter and stimulated hepatic T 4 outer ring deiodinase. Muscular thyroid hormone levels were preserved thanks to the PCB induced changes in T 4 dynamics. At 10 times higher concentrations (10 g 7PCBs per g food pellets) an important depression of T 3 and T 4 levels could be observed which are apparently caused by degenerative histological changes in the thyroid tissue.

Deiodinases and thyroid metabolism disruption in teleost fish

“…Thyroid disruption by PCBs seems to be mainly triggered by affecting the metabolism of T4, for instance increasing plasma T4 dynamics and glucuronidation. Studies in several teleosts show that exposure to PCB 77, 126 and Aroclor mixture hardly affect deiodination (Adams et al, 2000;Brar et al, 2010;Brown et al, 2004b;Schnitzler et al, 2012Schnitzler et al, , 2011Table 4), likely because the rest of the elements within the HPT axis are able to act in compensation.…”

Thyroid endocrine system disruption by pentachlorophenol: An in vitro and in vivo assay

“…PCP decreased the plasma T4 levels in rats (BruckerDavis, 1998;Kawaguchi et al, 2008). Decreased T4 levels are frequently observed in mammals, amphibian and fish models exposed to TH endocrine disruptors, e.g., PBDEs (Tomy et al, 2004;Ellis-Hutchings et al, 2006;Lema et al, 2008;Yu et al, 2010), PCBs (Donahue et al, 2004;Martin and Klaassen, 2010;Schnitzler et al, 2011), and perchlorates (Mukhi and Patino, 2007;Opitz et al, 2009;Schmidt et al, 2012). Decreased TT4 and increased TT3 levels and the consequent increased ratio of T3/T4 are frequently observed in fish exposed to TH endocrine disruptors (Chen et al, 2012;Wang et al, 2013).…”

Toxicological effects of clofibric acid and diclofenac on plasma thyroid hormones of an Indian major carp, Cirrhinus mrigala during short and long-term exposures

“…Moreover, thyroid disruption due to chemical toxicity may also result in the alterations of T 4 and T 3 (Li et al, 2014). Disruption of thyroid function by chemicals may affect the maintenance of a normal physiological status in vertebrates (Schnitzler et al, 2011). The previous literature indicates that the alterations of THs (TSH, T 4 and T 3 ) levels may be a result of a variety of mechanisms, such as tissue-specific alternations and THs related genes expressions (Li et al, 2009), changes in thyroid status and alterations in leasing its hormones (Oliveira et al, 2008), in process of biosynthesis and secretion of T 4 and T 3 (Capen, 1997), changes in hypothalamus or in pituitary status (Alkindi et al, 1996) and changes in hormone catabolism and clearance rates (Saito et al, 1991;Hontela et al, 1995).…”