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A METABOLOMIC APPROACH TO UNDERSTANDING ENDOCRINE DISRUPTION IN FATHEAD MINNOW
Citation:
EKMAN, D. R., T. W. COLLETTE, Q. TENG, G. T. ANKLEY, K. M. JENSEN, M. D. KAHL, AND D. L. VILLENEUVE. A METABOLOMIC APPROACH TO UNDERSTANDING ENDOCRINE DISRUPTION IN FATHEAD MINNOW. Presented at Metabolomics Society Annual Meeting, Boston, MA, June 24 - 28, 2006.
Impact/Purpose:
This task is divided into four major research areas: (1) Development of computational tools and databases for screening-level modeling of the environmental fate of organic chemicals; (2) Metabolism of xenobiotics: Enhancing the development of a metabolic simulator; (3) Metabonomics: The use of advanced analytical tools to identify toxicity pathways; and (4) Software infrastructure to support development and application of transformation/metabolic simulators.
For many chemicals, multiple transformation/metabolic pathways can exist. Consequently, transformation/metabolic simulators must utilize transformation rate data for prioritization of competing pathways. The prioritization process thus requires the integration of reliable rate data. When this data is absent, it is necessary to generate a database with metabolic and transformation rate constants based on: (1) experimentally measured values, including those requiring the use of advanced analytical techniques for measuring metabolic rate constants in vivo and in vitro; (2) rate constants derived from SPARC and mechanistic-based QSAR models; and (3) data mined from the literature and Program Office CBI. A long-term goal of this project is to build this database. This information will be used to enhance the predictive capabilities of the transformation/metabolic simulators. As indicated previously, exposure genomics, which provide early signs of chemical exposure based on changes in gene expression, will be used to guide chemical fate and metabolism studies. The incorporation of exposure genomics into fate studies will provide information concerning (1) the minimal concentrations at which biological events occur; and (2) the identification of biologically relevant chemicals(s) in mixtures.
The capability of categorizing chemicals and their metabolites based on toxicity pathway is imperative to the success of the CompTox Research Program. Metabonomics, which is the multi-parametric measurement of metabolites in living systems due to physiological stimuli and/or genetic modification, provides such a capability. The application of metabonomics to toxicity testing involves the elucidation of changes in metabolic patterns associated with chemical toxicity based on the measurement of component profiles in biofluids, and enables the generation of spectral profiles for a wide range of endogenous metabolites. Metabolic profiles can provide a measure of the real outcome of potential changes as the result of xenobiotic exposure.
Description:
Although widely used in the study of rodent toxicity responses to assess human risk, metabolomics is now finding utility in toxicity assessments in a wide variety of other organisms including environmentally relevant small fish species such as fathead minnow (FHM) and medaka. To better understand temporal and dose responses to endocrine-disrupting chemicals (EDCs) within the hypothalamic-pituitary-gonadal (HPG) axis of FHM, we have begun a series of 1H-NMR and MS-based metabolomics studies using multiple tissues and biofluids. Reported here are the results of an exposure conducted using a model EDC, 17 alpha-ethinylestradiol (EE2), at two dose levels, with 192 fish being sampled at a number of time points during exposure and after an eight day depuration phase. This approach has proven useful as a tool to characterize different responses relative to dose and time, including what appears to be a compensation effect to extended exposure to the high dose of EE2 (100ng/L). In addition, feminization of the male fish appears to be described by similarities of the metabolite profiles with those of control females. We have also begun to explore the use of fish urine to assess toxicity, as this provides the potential for conducting non-lethal sampling of an important biofluid of fish. This would allow us to assess responses from an individual fish over the time course of an exposure, making any metabolomic analyses potentially more meaningful. To this end, we have begun an exhaustive NMR assignment of metabolites observed in spectra generated for urine derived from control males. In addition, a small-scale exposure was conducted using the EDC vinclozolin, to determine the utility of using urine for toxicity assessment.