Mode of action analysis for fluxapyroxad-induced rat liver tumour formation: evidence for activation of the constitutive androstane receptor and assessment of human relevance.

Autor: Goettel M; BASF SE, Global Toxicology Agricultural Solutions, Speyerer Strasse 2, Limburgerhof 67117, Germany. Electronic address: manuela.goettel@basf.com., Werner C; BASF SE, Global Toxicology Agricultural Solutions, Speyerer Strasse 2, Limburgerhof 67117, Germany., Honarvar N; BASF SE, Experimental Toxicology and Ecology, Carl-Bosch-Strasse 38, Ludwigshafen am Rhein 67056, Germany., Gröters S; BASF SE, Experimental Toxicology and Ecology, Carl-Bosch-Strasse 38, Ludwigshafen am Rhein 67056, Germany., Fegert I; BASF SE, Global Toxicology Agricultural Solutions, Speyerer Strasse 2, Limburgerhof 67117, Germany., Haines C; Concept Life Sciences Ltd., 2, James Lindsay Place, Dundee Technopole, Dundee DD1 5JJ, United Kingdom., Chatham LR; Concept Life Sciences Ltd., 2, James Lindsay Place, Dundee Technopole, Dundee DD1 5JJ, United Kingdom., Vardy A; Concept Life Sciences Ltd., 2, James Lindsay Place, Dundee Technopole, Dundee DD1 5JJ, United Kingdom., Lake BG; School of Biosciences and Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK.
Jazyk: angličtina
Zdroj: Toxicology [Toxicology] 2024 Jun; Vol. 505, pp. 153828. Date of Electronic Publication: 2024 May 11.
DOI: 10.1016/j.tox.2024.153828
Abstrakt: The fungicide fluxapyroxad (BAS 700 F) has been shown to significantly increase the incidence of liver tumours in male Wistar rats at dietary levels of 1500 and 3000 ppm and in female rats at a dietary level of 3000 ppm via a non-genotoxic mechanism. In order to elucidate the mode of action (MOA) for fluxapyroxad-induced rat liver tumour formation a series of in vivo and in vitro investigative studies were undertaken. The treatment of male and female Wistar rats with diets containing 0 (control), 50, 250, 1500 and 3000 ppm fluxapyroxad for 1, 3, 7 and 14 days resulted in a dose-dependent increases in relative weight at 1500 and 3000 ppm from day 3 onwards in both sexes, with an increase in relative liver weight being also observed in male rats given 250 ppm fluxapyroxad for 14 days. Examination of liver sections revealed a centrilobular hepatocyte hypertrophy in some fluxapyroxad treated male and female rats. Hepatocyte replicative DNA synthesis (RDS) was significantly increased in male rats given 1500 and 3000 ppm fluxapyroxad for 3 and 7 days and in female rats given 50-3000 ppm fluxapyroxad for 7 days and 250-3000 ppm fluxapyroxad for 3 and 14 days; the maximal increases in RDS in both sexes being observed after 7 days treatment. The treatment of male and female Wistar rats with 250-3000 ppm fluxapyroxad for 14 days resulted in significant increases in hepatic microsomal total cytochrome P450 (CYP) content and CYP2B subfamily-dependent enzyme activities. Male Wistar rat hepatocytes were treated with control medium and medium containing 1-100 μM fluxapyroxad or 500 μM sodium phenobarbital (NaPB) for 4 days. Treatment with fluxapyroxad and NaPB increased CYP2B and CYP3A enzyme activities and mRNA levels but had little effect on markers of CYP1A and CYP4A subfamily enzymes and of the peroxisomal fatty acid β-oxidation cycle. Hepatocyte RDS was significantly increased by treatment with fluxapyroxad, NaPB and 25 ng/ml epidermal growth factor (EGF). The treatment of hepatocytes from two male human donors with 1-100 μM fluxapyroxad or 500 μM NaPB for 4 days resulted in some increases in CYP2B and CYP3A enzyme activities and CYP mRNA levels but had no effect on hepatocyte RDS, whereas treatment with EGF resulted in significant increase in RDS in both human hepatocyte preparations. Hepatocytes from male Sprague-Dawley wild type (WT) and constitutive androstane receptor (CAR) knockout (CAR KO) rats were treated with control medium and medium containing 1-16 μM fluxapyroxad or 500 μM NaPB for 4 days. While both fluxapyroxad and NaPB increased CYP2B enzyme activities and mRNA levels in WT hepatocytes, only minor effects were observed in CAR KO rat hepatocytes. Treatment with both fluxapyroxad and NaPB only increased RDS in WT and not in CAR KO rat hepatocytes, whereas treatment with EGF increased RDS in both WT and CAR KO rat hepatocytes. In conclusion, a series of in vivo and in vitro investigative studies have demonstrated that fluxapyroxad is a CAR activator in rat liver, with similar properties to the prototypical CAR activator phenobarbital. A robust MOA for fluxapyroxad-induced rat liver tumour formation has been established. Based on the lack of effect of fluxapyroxad on RDS in human hepatocytes, it is considered that the MOA for fluxapyroxad-induced liver tumour formation is qualitatively not plausible for humans.
Competing Interests: Declaration of Competing Interest M. Goettel, C. Werner, N. Honarvar, S. Gröters, and I. Fegert are all employed by BASF, which manufactures fluxapyroxad. All other authors have been involved in studies on fluxapyroxad funded by BASF. The authors alone are responsible for the content and writing of this article. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2024 Elsevier B.V. All rights reserved.)
Databáze: MEDLINE
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