Nanometals induce stress and alter thyroid hormone action in amphibia at or below North American water quality guidelines.

Nanometals are manufactured to particle sizes with diameters in the nanometer range and are included in a variety of consumer and health products. There is a lack of information regarding potential effects of these materials on aquatic organisms. Amphibians are regarded as environmental sentinels and demonstrate an exquisite sensitivity to thyroid hormone action, a hormone that is essential for human health. This present study assessed the effect of exposure to nanometals on stress and thyroid hormone signaling in frog tissue using a cultured tail fin biopsy (C-fin) assay derived from Rana catesbeiana tadpoles. The C-fin assay maintains tissue complexity and biological replication while multiple chemical responses can be assessed from the same individual. We tested the ability of nanosilver (0.06 µg/L-5.5 mg/L), quantum dots (0.25 µg/L-22 mg/L), and nanozinc oxide (0.19-10 mg/L) to alter gene expression in the presence or absence of 3,3',5'-triiodothyronine (T(3)) using quantitative real-time polymerase chain reaction. Results were compared to exposure to micrometer-silver, silver nitrate, and micrometer-cadmium telluride. Nanosilver (≥2.75 mg/L) and quantum dots (≥0.22 mg/L) altered the expression of transcripts linked to T(3)- and stress-mediated pathways, while nanozinc oxide had no effect. Lower concentrations of nanosilver (0.6 to 550 µg/L) perturbed T(3)-mediated signaling while not inducing cell stress. The observed effects were orders of magnitude below acute toxicity levels and occurred at or below the current North American water quality guidelines for metals, underscoring the need for evaluating nanoparticles separately from their constituent chemicals.

C-fin: a cultured frog tadpole tail fin biopsy approach for detection of thyroid hormone-disrupting chemicals.

There is a need for the development of a rapid method for identifying chemicals that disrupt thyroid hormone (TH) action while maintaining complex tissue structure and biological variation. Moreover, no assay to date allows a simultaneous screen of an individual's response to multiple chemicals. A cultured tail fin biopsy or C-fin assay was developed using Rana catesbeiana tadpoles. Multiple tail fin biopsies were taken per tadpole, cultured in serum-free medium, and then each biopsy was exposed to a different treatment condition. The effects of known disruptors of TH action were evaluated in the C-fin assay. Chemical exposure was performed +/- 10 nM 3,3',5-triiodothyronine and real-time quantitative polymerase chain reaction (QPCR) of two TH-responsive transcripts, TH receptor beta (TRbeta) and the Rana larval keratin type I (RLKI), was performed. Within 48 h of exposure to Triac (1-100 nM), roscovitine (0.6-60 microM), or genistein (1-100 microM), perturbations in TH signaling were detected. Tetrabromobisphenol A (TBBPA) (10-1,000 nM) showed no effect. Acetochlor (1-100 nM) elicited a modest effect on the TH-dependent induction of TRbeta transcript. These data reveal that a direct tissue effect may not be critical for TBBPA and acetochlor to disrupt TH action previously observed in intact tadpoles.