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CROSS-SPECIES COMPARISON OF CONAZOLE FUNGICIDE METABOLITES USING RAT AND RAINBOW TROUT (ONCHORHYNCHUS MYKISS) HEPATIC MICROSOMES AND PURIFIED HUMAN CYTOCHROME P450 3A4
Citation:
MAZUR, C. S. AND J. F. KENNEKE. CROSS-SPECIES COMPARISON OF CONAZOLE FUNGICIDE METABOLITES USING RAT AND RAINBOW TROUT (ONCHORHYNCHUS MYKISS) HEPATIC MICROSOMES AND PURIFIED HUMAN CYTOCHROME P450 3A4. Presented at 8th International Society for the Study of Xenobiotics, Sendai, JAPAN, October 09 - 12, 2007.
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:
Conazoles represent a unique class of azole-containing fungicides that are widely used in both pharmaceutical and agriculture applications. The antifungal property of conazoles occurs via complexation with cytochrome P450 monooxygenases (CYP) responsible for mediating fungal cell wall synthesis. This CYP-directed mode of action has cause for concern in vertebrate species with regards to inhibiting a broad spectrum of CYP-detoxifying mechanisms. Most toxicological screening assays are designed with mammalian (rodent) receptors or tissues, thus a major complication for environmental risk assessment is the degree of cross-species extrapolation used from mammalian to aquatic systems. Although inherently complex, metabolite identification is critical to risk assessment since products formed may pose a greater toxicological threat than the parent molecule. In this report, LC/MS and LC-MS/MS were implemented to determine in vitro metabolic profiles for thirteen different conazoles using rat and rainbow trout (Oncorhynchus mykiss) hepatic microsomes and purified human CYP 3A4. Our results indicate that rat and trout interspecies metabolite comparison of conazole fungicides was well conserved via both aromatic and aliphatic hydroxylation and carbonyl reduction processes. In addition, biotransformation screening clearly indicates that the phase I mode of action observed with human CYP 3A4 was strongly correlated to that of both rat and trout microsomes.