tretinoin and propiconazole

The field of mechanistic chemical carcinogenesis has evolved with the advent and advances in genomic, proteomic and metabolomic technologies. These advances allow mechanistic events along the process of exposure to frank tumors to be studied in great detail. Herein is reviewed an example of this approach using, propiconazole, a triazole-containing antifungal agent that is a mouse hepatocarcinogen. This review will highlight those toxicological, genomic, proteomic and metabolomic findings in mice that were used to describe a set of linked events that lead to propiconazole-induced hepatocarcinogenesis. Independent experimental proof of many of these events is presented that solidified this proposed mechanism of carcinogenic action for propiconazole.

Topics: Animals; Carcinogens; Cell Proliferation; Cholesterol; Cytochrome P-450 Enzyme System; DNA Adducts; Feedback, Physiological; Genomics; Liver; Liver Neoplasms, Experimental; Metabolome; Mice; Mutation; Oxidative Stress; Proteomics; Reactive Oxygen Species; Toxicology; Tretinoin; Triazoles

Conazoles are fungicides used in agriculture and as pharmaceuticals. In a previous toxicogenomic study of triazole-containing conazoles we found gene expression changes consistent with the alteration of the metabolism of all trans-retinoic acid (atRA), a vitamin A metabolite with cancer-preventative properties (Ward et al., Toxicol. Pathol. 2006; 34:863-78). The goals of this study were to examine effects of propiconazole, triadimefon, and myclobutanil, three triazole-containing conazoles, on the microsomal metabolism of atRA, the associated hepatic cytochrome P450 (P450) enzyme(s) involved in atRA metabolism, and their effects on hepatic atRA levels in vivo. The in vitro metabolism of atRA was quantitatively measured in liver microsomes from male CD-1 mice following four daily intraperitoneal injections of propiconazole (210 mg/kg/d), triadimefon (257 mg/kg/d) or myclobutanil (270 mg/kg/d). The formation of both 4-hydroxy-atRA and 4-oxo-atRA were significantly increased by all three conazoles. Propiconazole-induced microsomes possessed slightly greater metabolizing activities compared to myclobutanil-induced microsomes. Both propiconazole and triadimefon treatment induced greater formation of 4-hydroxy-atRA compared to myclobutanil treatment. Chemical and immuno-inhibition metabolism studies suggested that Cyp26a1, Cyp2b, and Cyp3a, but not Cyp1a1 proteins were involved in atRA metabolism. Cyp2b10/20 and Cyp3a11 genes were significantly over-expressed in the livers of both triadimefon- and propiconazole-treated mice while Cyp26a1, Cyp2c65 and Cyp1a2 genes were over-expressed in the livers of either triadimefon- or propiconazole-treated mice, and Cyp2b10/20 and Cyp3a13 genes were over-expressed in the livers of myclobutanil-treated mice. Western blot analyses indicated conazole induced-increases in Cyp2b and Cyp3a proteins. All three conazoles decreased hepatic atRA tissue levels ranging from 45-67%. The possible implications of these changes in hepatic atRA levels on cell proliferation in the mouse tumorigenesis process are discussed.

Topics: Animals; Blotting, Western; Body Weight; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme System; Fungicides, Industrial; Gene Expression Profiling; Liver; Male; Mice; Microsomes, Liver; Nitriles; Organ Size; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Spectrometry, Mass, Electrospray Ionization; Tretinoin; Triazoles