The nuclear receptors pregnane X receptor and constitutive androstane receptor contribute to the impact of fipronil on hepatic gene expression linked to thyroid hormone metabolism

Abstract

Fipronil is described as a thyroid disruptor in rat. Based on the hypothesis that this results from a perturbation of hepatic thyroid hormone metabolism, our goal was to investigate the pathways involved in fipronil-induced liver gene expression regulations. First, we performed a microarray screening in the liver of rats treated with fipronil or vehicle. Fipronil treatment led to the upregulation of several genes involved in the metabolism of xenobiotics, including the cytochrome P450 Cyp2b1, Cyp2b2 and Cyp3a1, the carboxylesterases Ces2 and Ces6, the phase II enzymes Ugt1a1, Sult1b1 and Gsta2, and the membrane transporters Abcc2, Abcc3, Abcg5, Abcg8, Slco1a1 and Slco1a4. Based on a large overlap with the target genes of constitutive androstane receptor (CAR) and pregnane X receptor (PXR), we postulated that these two nuclear receptors are involved in mediating the effects of fipronil on liver gene expression in rodents. We controlled that liver gene expression changes induced by fipronil were generally reproduced in mice, and then studied the effects of fipronil in wild-type, CAR- and PXR-deficient mice. For most of the genes studied, the gene expression modulations were abolished in the liver of PXR-deficient mice and were reduced in the liver of CAR-deficient mice. However, CAR and PXR activation in mouse liver was not associated with a marked increase of thyroid hormone clearance, as observed in rat. Nevertheless, our data clearly indicate that PXR and CAR are key modulators of the hepatic gene expression profile following fipronil treatment which, in rats, may contribute to increase thyroid hormone clearance.

Keywords: (13)C(6)-levothyroxine (PubChem CID: 53442260); 5′-diphospho (UDP)-glucuronosyltransferase; ATP-binding cassette; Abc; CAR; Ces; Constitutive androstane receptor; Cyp; ESI(+); FT3; FT4; Fipronil; Fipronil (PubChem CID: 3352); GABA; GEO; GO; Gst; Hepatic metabolism; LOQ; MRM; MRP; OATP; PB; PCN; PXR; Polr2a; Pregnane X receptor; QC; RNA polymerase II polypeptide A; RT-qPCR; Rodents; Slco; Sult; T3; T4; TATA-box binding protein; TSH; TT3; TT4; Tbp; Thyroid hormone metabolism; Thyroxine (PubChem CID: 5819); Triiodothyronine (PubChem CID: 5920); Ugt; carboxylesterase; constitutive androstane receptor; cytochrome P450; electrospray ionization mode; free thyroxine; free triiodothyronine; gene expression omnibus; gene ontology; glutathione S-transferase; limit of quantification; multidrug resistance-associated protein; multiple reaction monitoring; organic anion-transporting polypeptide; phenobarbital; pregnane X receptor; pregnenolone-16alpha-carbonitrile; quality control; real-time quantitative polymerase chain reaction; solute carrier organic anion transporter; sulfotransferase; thyroid-stimulating hormone; thyroxine; total thyroxine; total triiodothyronine; triiodothyronine; γ-aminobutyric acid.