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Cytotoxic effects of propiconazole and its metabolites in mouse and human hepatoma cells and primary mouse hepatocytes
Citation:
Chen, P., T. MOORE, AND S. NESNOW. Cytotoxic effects of propiconazole and its metabolites in mouse and human hepatoma cells and primary mouse hepatocytes. TOXICOLOGY IN VITRO. Elsevier Science Ltd, New York, NY, 22(6):1476 - 1483, (2008).
Impact/Purpose:
The study is a product of the ORD Conazole Research Program which is studying how this class of fungicides induces cancer in mice and possibly in humans. We investigated whether metabolism of propiconazole was a toxification or detoxification event as part of our mode of action studies.
Description:
Abstract: Propiconazole is a triazole-containing fungicide that is used agriculturally on grasses, fruits, grains, seeds, hardwoods, and conifers. Propiconazole is a mouse liver hepatotoxicant and a hepatocarcinogen and has adverse reproductive and developmental toxicities in experimental animals. The aim of this study was to investigate the cytotoxic effects of propiconazole and five of its metabolites in three hepatic cell types: the mouse hepatoma Hepa1c1c7 cell line, the human hepatoma HepG2 cell line, and primary cultures of mouse hepatocytes. Propiconazole induced concentration-related cytotoxic responses in both Hepa1c1c7 and HepG2 cell lines over a concentration range of 0-200 μM after a 24-h exposure in using two assay systems: the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and the Neutral red assay. The relative hepatocytotoxicity of propiconazole and five propiconazole metabolites were further assessed by the MTT assay using Hepa1c1c7 and HepG2 cell lines and in primary mouse hepatocytes. The cell cultures were exposed from 24-48 h to various concentrations of propiconazole and five of its metabolites over a range of 0 to 400 μM. Propiconazole was cytotoxic in all three cell types in a dose-dependent manner with CC50 values of 85.4 μM in Hepa1c1c7 cells, 148.4 μM in HepG2 cells and 175.5 μM in primary mouse hepatocytes. All five metabolites were less cytotoxic in all three cell types compared to the parent compound. The most cytotoxic metabolites in Hepa1c1c7 and HepG2 cells among the five were 3-(2-((1H-1,2,4-triazol-1-yl)methyl)-2-(2,4-dichlorophenyl)-1,3-dioxolan-4-yl)propan-1-ol and 1-(2-((1H-1,2,4-triazol-1-yl)methyl)-2- (2,4-dichlorophenyl)-1,3-dioxolan-4-yl)propan-2-ol. None of the metabolites were cytotoxic in primary mouse hepatocytes. There was a linear relationship between the cytotoxicity of propiconazole and the five metabolites in Hepa1c1c7 cells and their calculated LogP values. These results demonstrate that while propiconazole was cytotoxic in the three hepatic cell types, three of the metabolites were only cytotoxic in the hepatoma cells and required higher concentrations to exert the same cytotoxic effects as propiconazole. These results suggest that these propiconazole metabolites would not contribute to the propiconazole induced cytotoxicity process in primary mouse hepatocytes. Our results using hepatotumorigenic cells lines suggest that in the tumorigenesis process as tumor cells are formed they would be more susceptible to the cytotoxic effects of propiconazole than to the propiconazole metabolites.
What is the study?
Propiconazole is a triazole-containing fungicide that is used agriculturally on grasses, fruits, grains, seeds, hardwoods, and conifers. Propiconazole is a mouse liver hepatotoxicant and a hepatocarcinogen and has adverse reproductive and developmental toxicities in experimental animals. The aim of this study was to investigate the cytotoxic effects of propiconazole and five of its metabolites in three hepatic cell types: the mouse hepatoma Hepa1c1c7 cell line, the human hepatoma HepG2 cell line, and primary cultures of mouse hepatocytes.
Why was it done?
The study is a product of the ORD Conazole Research Program which is studying how this class of fungicides induces cancer in mice and possibly in humans. We investigated whether metabolism of propiconazole was a toxification or detoxification event as part of our mode of action studies.
What is the impact to the field and the Agency?
Many environmental conazoles that the Agency regulates induce cancer in mice. At present the modes of action of these agents are unknown and the Agency relies on default assumptions to make decision on their cancer risk assessments. The ORD Conazole Research Program seeks to replace these default assumptions with scientific defensible data.