In vivo assessment and potential diagnosis of xenobiotics that perturb the thyroid pathway: Proteomic analysis of Xenopus laevis brain tissue following exposure to model T4 inhibitors

As part of a multi-endpoint systems approach to develop comprehensive methods for assessing endocrine stressors in vertebrates, differential protein profiling was used to investigate expression patterns in the brain of the amphibian model (Xenopus laevis) following in vivo exposure to a suite of T4 synthesis inhibitors. We specifically address the application of Two Dimensional Polyacrylamide Gel Electrophoresis (2D PAGE), Isobaric Tags for Relative and Absolute Quantitation (iTRAQ®) and LC–MS/MS to assess changes in relative protein expression levels. 2D PAGE and iTRAQ proved to be effective complementary techniques for distinguishing protein changes in the developing amphibian brain in response to T4 synthesis inhibition. This information served to evaluate the use of distinctive protein profiles as a potential mechanism to screen chemicals for endocrine activity in anurans. Regulatory pathways associated with proteins expressed as a result of chemical effect are reported. To our knowledge, this is also the first account of the anuran larvae brain proteome characterization using proteomic technologies. Correlation of protein changes to other cellular and organism-level responses will aid in the development of a more rapid and cost-effective, non-mammalian screening assay for thyroid axis-disrupting chemicals.