Triclosan exposure alters postembryonic development in a Pacific tree frog (Pseudacris regilla) Amphibian Metamorphosis Assay (TREEMA)

The Amphibian Metamorphosis Assay (AMA), developed for Xenopus laevis, is designed to identify chemicals that disrupt thyroid hormone (TH)-mediated biological processes. We adapted the AMA for use on an ecologically-relevant North American species, the Pacific tree frog (Pseudacris regilla), and applied molecular endpoints to evaluate the effects of the antibacterial agent, triclosan (TCS). Premetamorphic (Gosner stage 26-28) tadpoles were immersed for 21 days in solvent control, 1.5 mu g/L thyroxine (T-4), 0.3, 3 and 30 mu g/L (nominal) TCS, or combined T-4/TCS treatments. Exposure effects were scored by morphometric (developmental stage, wet weight, and body, snout-vent and hindlimb lengths) and molecular (mRNA abundance using quantitative real time polymerase chain reaction) criteria. T-4 treatment alone accelerated development concomitant with altered levels of TH receptors alpha and beta, proliferating cell nuclear antigen, and gelatinase B mRNAs in the brain and tail. We observed TCS-induced perturbations in all of the molecular and morphological endpoints indicating that TCS exposure disrupts coordination of postembryonic tadpole development. Clear alterations in molecular endpoints were evident at day 2 whereas the earliest morphological effects appeared at day 4 and were most evident at day 21. Although TCS alone (3 and 30 mu g/L) was protective against tadpole mortality, this protection was lost in the presence of T-4. The Pacific tree frog is the most sensitive species examined to date displaying disruption of TH-mediated development by a common antimicrobial agent. (C) 2012 Elsevier B.V. All rights reserved.