Citation:

Haselman, J., M. Sakurai, N. Watanabe, Y. Goto, Y. Onishi, Y. Ito, Y. Onoda, Pat Kosian, Joe Korte, R. Johnson, T. Iguchi, AND S. Degitz. Development of the larval amphibian growth and development assay: Effects of benzophenone-2 exposure in Xenopus laevis from embryo to juvenile. JOURNAL OF APPLIED TOXICOLOGY. John Wiley & Sons, Ltd., Indianapolis, IN, 36(12):1651-1661, (2016).

Impact/Purpose:

This manuscript will be the second peer-reviewed journal article that presents methods and results from the EDSP Tier II Larval Amphibian Growth and Development Assay developed here at MED. This agency guideline is in the final stages of review within EPA and was recently officially adopted by OECD as a globally harmonized testing method. This study was performed by Japanese collaborators demonstrating the utility and transferability of the test guideline, which is anticipated to be finalized and implemented in 2015. In addition, the results presented in this manuscript will serve as precedent for the suite of endocrine effects observed following exposure to a mixed mode of action environmental chemical in amphibians. Endocrine effects characterized in this study may be observed from future chemicals tested using the LAGDA under OCSPP/OSCP/EFED oversight.

Description:

The Larval Amphibian Growth and Development Assay (LAGDA) is a globally harmonized chemical testing guideline developed by the U.S. Environmental Protection Agency in collaboration with Japan’s Ministry of Environment to support risk assessment. The assay is employed as a higher tiered approach to evaluate effects of chronic chemical exposure throughout multiple life stages in model amphibian species Xenopus laevis. To evaluate the utility of the initial LAGDA design, the assay was performed using a mixed mode of action endocrine disrupting chemical, benzophenone-2 (BP-2). X. laevis embryos were exposed in flow-through conditions to 0, 1.5, 3.0 or 6.0 mg/L BP-2 until two months post-metamorphosis. Overt toxicity was evident throughout the exposure period in the 6.0 mg/L treatment due to elevated mortality rates and observed liver and kidney pathologies. Concentration-dependent increases in severity of thyroid follicular cell hypertrophy and hyperplasia occurred in larval tadpoles indicating BP-2-induced impacts on the thyroid axis. Additionally, gonads were impacted in all treatments with some genotypic males showing both testis and ovary tissues (1.5 mg/L) and 100% of the genotypic males in the higher treatments (3.0 and 6.0 mg/L) experiencing complete male-to-female sex reversal. Concentration-dependent vitellogenin (Vtg) induction occurred in both genders with associated accumulations of protein in the livers, kidneys and gonads, which was likely Vtg and other estrogen-responsive yolk precursors. This is the first study that demonstrates the endocrine effects of this mixed mode of action chemical in an amphibian species and also demonstrates the utility of the LAGDA design for supporting chemical risk assessment.

URLs/Downloads:

Record Details: