Triclocarban Mediates Induction of Xenobiotic Metabolism through Activation of the Constitutive Androstane Receptor and the Estrogen Receptor Alpha

Abstract

Triclocarban (3,4,4′-trichlorocarbanilide, TCC) is used as a broad-based antimicrobial agent that is commonly added to personal hygiene products. Because of its extensive use in the health care industry and resistance to degradation in sewage treatment processes, TCC has become a significant waste product that is found in numerous environmental compartments where humans and wildlife can be exposed. While TCC has been linked to a range of health and environmental effects, few studies have been conducted linking exposure to TCC and induction of xenobiotic metabolism through regulation by environmental sensors such as the nuclear xenobiotic receptors (XenoRs). To identify the ability of TCC to activate xenobiotic sensors, we monitored XenoR activities in response to TCC treatment using luciferase-based reporter assays. Among the XenoRs in the reporter screening assay, TCC promotes both constitutive androstane receptor (CAR) and estrogen receptor alpha (ERα) activities. TCC treatment to hUGT1 mice resulted in induction of the UGT1A genes in liver. This induction was dependent upon the constitutive active/androstane receptor (CAR) because no induction occurred in hUGT1Car−/− mice. Induction of the UGT1A genes by TCC corresponded with induction of Cyp2b10, another CAR target gene. TCC was demonstrated to be a phenobarbital-like activator of CAR in receptor-based assays. While it has been suggested that TCC be classified as an endocrine disruptor, it activates ERα leading to induction of Cyp1b1 in female ovaries as well as in promoter activity. Activation of ERα by TCC in receptor-based assays also promotes induction of human CYP2B6. These observations demonstrate that TCC activates nuclear xenobiotic receptors CAR and ERα both in vivo and in vitro and might have the potential to alter normal physiological homeostasis. Activation of these xenobiotic-sensing receptors amplifies gene expression profiles that might represent a mechanistic base for potential human health effects from exposure to TCC.

The commonly used antimicrobial additive triclosan is a liver tumor promoter

“…The activity of mouse XenoRs, including pregnane X receptor (PXR), CAR, liver X receptor α (LXR α), farnesoid X receptor (FXR), vitamin D receptor (VDR), PPARα, PPARβ, PPARγ, estrogen receptor α (ERα), ERβ, and glucocorticoid receptor (GR) in response to TCS (10 μM) was monitored. CV-1 cells were maintained in DMEM (Life Technologies) supplemented with 10% FBS, seeded in 96-well plates, and transfected with an expression vector containing a specific nuclear receptor (i.e., PXR, CAR, LXRα, VDR, FXR, PPARα, PPARδ, PPARγ, or GR) and RXR, along with a luciferase reporter containing the appropriate DNA response element, as described previously (9). The assay was first validated with known nuclear receptor ligands as positive controls, including pregnenolone 16α-carbonitrile (10 μm; Sigma) for PXR, 1,4-bis-[2-(3,5-dichloropyridyloxy)]benzene (250 nM; Sigma) for CAR, β-estradiol (10 nM; Sigma) for ER, T0901317 (1 μM; CAYMAN Chemical) for LXRα, calcipotriol (10 μM; Sigma) for VDR, GW4064 (1 μM; Sigma) for FXR, WY14643 (30 μM; Sigma) for PPARα, GW501516 (100 nM) for PPARδ, rosiglitazone (1 μM; Cayman Chemical) for PPARγ, and dexamethasone (100 nM; Sigma) for GR.…”

“…Before testing the hypothesis, that the profibrogenic effect of TCS would ultimately lead to liver carcinogenesis, we examined whether TCS activates PPARα, as previously suggested (2). We monitored activities of a series of mouse XenoRs, including PXR, CAR, LXRα, FXR, VDR, PPARα, PPARβ, PPARγ, ERα, ERβ, and GR, and validated the assay by using a positive ligand for each nuclear receptor, as detailed previously (9). Of the 11 XenoRs screened with TCS (10 μm), only CAR was modestly activated by TCS (Fig.…”

Different action of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and its hydroxylated metabolites on ERα and ERβ gene and protein expression

“…Using CAR null mice, Yueh et al (2012) showed ER␣-dependent induction of CYP2B10 in livers of animals exposed to triclocarban (TCC), an antimicrobial agent commonly added to personal hygiene products. These authors, using luciferase-based reporter assays also demonstrated that triclocarban (TCC) promotes induction of human CYP2B6 by ER␣ in MCF7 cells (Yueh et al, 2012).…”

Review: <i>Pharmaceutical and personal care products (PPCPs) as endocrine disrupting contaminants (EDCs) in South African surface waters</i>

“…Although the endocrine disrupting effect of the biocide TCS has been well documented, and also found at high concentrations in the environment (Table 1, Halden and Paull, 2005), limited data are available on the endocrine-disrupting effect of TCC. Exposure to TTC in human cell-based bioassays, and exposure of rodents to TTC, indicated that the biocide does not have endocrine-disrupting activity on its own, but rather enhances the action and binding affinity of steroid hormones (Table 2; Ahn et al, 2008;Chen et al, 2008;Christen et al, 2010;Yueh et al, 2012). This shows a potentiating mechanism of endocrine disruption, as well as an alternative mode of endocrine disruption other than direct modulation of endocrine pathways.…”