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METABOLOMIC EVALUATION OF RAT LIVER AND TESTIS TO CHARACTERIZE THE TOXICITY OF TRIAZOLE FUNGICIDES
Citation:
EKMAN, D. R., H. C. KEUN, C. D. EADS, C. M. FURNISH, R. N. MURRELL, J. C. ROCKETT, AND D. J. DIX. METABOLOMIC EVALUATION OF RAT LIVER AND TESTIS TO CHARACTERIZE THE TOXICITY OF TRIAZOLE FUNGICIDES. Metabolomics. Plenum Press, New York, NY, 2(2):63-73, (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:
The effects of two triazole fungicides, myclobutanil and triadimefon, on endogenous rat metabolite profiles in blood serum, liver, and testis was assessed using proton nuclear magnetic resonance (1H-NMR) spectroscopy. Adult male Sprague-Dawley rats were dosed daily by gavage for 14 days with myclobutanil or triadimefon, at two dose levels for each triazole. Following exposure, serum, liver, and testis were collected and processed for NMR analysis. Principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA) of the resulting spectra were used to determine changes in metabolite profiles as a result of exposure. Using this approach, responses common to both triazoles were identified, as well as responses indicative of differences in the toxicity of these two compounds. Although changes were observed in serum metabolites following exposure, none were robust enough to be considered a biomarker of exposure/effect. A number of metabolic changes were, however, observed in the liver with both triazoles, particularly in metabolites related to the methionine cycle. The testes of myclobutanil-exposed animals displayed altered levels of creatine and creatinine, consistent with testicular toxicity. Overall, the results of this study support the possible application of a metabolomics approach to assessing the toxicity of triazole fungicides and identifying biomarkers of exposure and/or effect.