Waterborne exposure to microcystin‐LR causes thyroid hormone metabolism disturbances in juvenile Chinese rare minnow (Gobiocypris rarus)

Abstract

Microcystin-LR (MC-LR) has the potential to disturb thyroid hormone homeostasis, but little is known about the underlying mechanisms of MC-LR in fish. In the present study, juvenile Chinese rare minnows (Gobiocypris rarus) were exposed to various concentrations of MC-LR (0 µg/L, 50 µg/L, 100 µg/L, and 500 µg/L) for 7 d. The whole-body thyroid hormone content, the histology of thyroid follicle epithelial cells, the activities of hepatic iodothyronine deiodinases, and the transcription of selected genes associated with thyroid hormone synthesis, transport, and metabolism were analyzed. Following exposure to MC-LR, whole-body concentrations of both thyroxine (T4 ) and triiodothyronine (T3 ) were significantly decreased. The levels of messenger RNA for sodium/iodide symporter, transthyretin, thyroid hormone receptor-α, iodothyronine deiodinase2, and iodothyronine deiodinase3 were significantly down-regulated after exposure to 500 µg/L MC-LR. A significant decrease in ID2 activity was also observed in the 500-µg/L MC-LR exposure group. Moreover, hypertrophy of thyroid follicle epithelial cells was observed after exposure to MC-LR. The results indicate that acute MC-LR exposure has the potential to disturb the homeostasis of thyroid hormone metabolism, leading to a hypothyroidism state in the juvenile Chinese rare minnow.

A review of reproductive toxicity of microcystins

“…Besides modulating the HPG axis, it has also been previously demonstrated that MCs alter the metabolism of cortisol and thyroid hormone, through activating the hypothalamic-pituitary-adrenal/interrenal (for fish) (HPA/HPI) and hypothalamic-pituitary-thyroid (HPT) axis [130][131][132][133][134][135][136]. As mentioned above, the endocrine system is very complex and affected by many factors, and previous studies have shown that liver damage may not only induce sex hormone changes [127], but also reduce hepatic thyroxine deiodination in animals [137], which in turn causes a decline in peripheral triiodothyronine production [130].…”

Effects of toxic cyanobacteria and ammonia on flesh quality of blunt snout bream (Megalobrama amblycephala)

“…The typical toxic mechanism of MCs is to inhibit protein phosphatase 1 and 2A, resulting in oxidative stress . Studies have shown that MCs appear to exert negative effects on the growth, development, reproduction, behavior, immune function and endocrine systems of various species of fish . Additionally, MCs can be bioaccumulated in aquatic animals and transferred along the food chain.…”