Triclosan elevates estradiol levels in serum and tissues of cycling and peri-implantation female mice

Highlights

• We examined the effect of triclosan on estradiol concentrations in female mice.

• Triclosan exposure increased the presence in tissues of exogenous ³H-estradiol.

• Triclosan exposure produced elevated urinary estradiol concentrations.

• These data may be pertinent to anti-reproductive and carcinogenic effects.

Abstract

Triclosan, an antimicrobial agent added to personal care products, can modulate estrogenic actions. We investigated whether triclosan affects concentrations of exogenous and endogenous estradiol. Female mice were given injections of triclosan followed by 1 μCi tritium-labeled estradiol. Mice given daily 2-mg triclosan doses (57.9 mg/kg/dose) showed significantly elevated radioactivity in tissues and serum compared to controls. A single dose of 1 or 2 mg triclosan increased radioactivity in the uterus in both cycling and peri-implantation females. We also measured natural urinary estradiol at 2–12 h following triclosan injection. Unconjugated estradiol was significantly elevated for several hours following 1 or 2 mg of triclosan. These data are consistent with evidence that triclosan inhibits sulfonation of estrogens by interacting with sulfotransferases, preventing metabolism of these steroids into biologically inactive forms. Elevation of estrogen concentrations by triclosan is potentially relevant to anti-reproductive and carcinogenic actions of excessive estrogen activity.

Introduction

Triclosan (CAS 3380-34-5) is a synthetic biocide designed to inhibit bacterial reproduction by interacting with enoyl-acyl carrier protein reductase enzymes [1]. It is added to many consumer and household products, including soaps, dish sponges, cosmetics, deodorants, toothpastes, mouthwashes, clothing, and children’s toys [2], [3], [4]. Dermal contact with these products leads to rapid absorption of triclosan into the body through the skin [5], [6], while oral ingestion leads to uptake through the gastrointestinal tract [7]. Based on the 2003–2004 U.S. National Health and Nutrition Examination Survey (NHANES), 74.6% of the 2517 human urine samples contained detectable levels of triclosan, with concentrations ranging from 2.4 to 3790 μg/l [8]. Detection frequency of urinary triclosan in the U.S. population reached a peak between 2007 and 2008 at 80.8%, but has since fallen to 72.0% as of 2011–2012 [9]. Similarly, mean urinary triclosan concentrations in the U.S. population peaked in 2005–2006 at 18.8 μg/L but fell to 12.46 μg/l as of 2011–2012 [9]. Triclosan has also been detected in human serum [10], [11], plasma [12], breast milk [12], [13], and adipose and liver tissue [14].

Triclosan has known estrogenic effects, including stimulating breast and ovarian cancer cell growth in vitro [15], [16] and magnifying the effects of ethinyl estradiol in rodent uterotrophic assays [17], [18]. However, the mechanisms underlying these effects are not well understood. Triclosan binds to both conventional estrogen receptor (ER) subtypes, ERα and ERβ [19], [20]. Thus, exposure to triclosan may induce estrogenic effects by directly activating ER. Triclosan also potently inhibits hepatic sulfotransferase activity [21], [22], [23], thereby reducing sulfonation of endogenous estrogens such as 17β-estradiol (E₂) and xenoestrogens such as bisphenol A (BPA) [23]. Thus, exposure to triclosan may potentiate in vivo estrogenic effects by preventing metabolism of estrogens to their biologically inactive forms.

Previous work in this laboratory demonstrated in vivo interactions between triclosan and BPA. When mice were given a single dose of triclosan ranging from 0.2–18 mg, greater levels of ¹⁴C-BPA were detected in serum and tissues including the heart, lung, muscle, uterus, ovaries, and epididymides, than in animals given ¹⁴C-BPA alone [24]. Other studies indicated that either triclosan or BPA can disrupt blastocyst implantation in inseminated female mice [25], [26], [27], [28], [29], and that doses of BPA or triclosan that were insufficient on their own to have effects could disrupt implantation when the two substances were given concurrently [29]. These findings are consistent with the notion that triclosan inhibits BPA conjugation [23], permitting higher levels of BPA to interact with ER in tissues such as the uterus.

Whereas BPA is a weakly estrogenic environmental chemical, E₂ is the most potent natural estrogen. Any deviations from normal E₂ levels might lead to adverse health effects, as estrogen levels are tightly regulated and play critical roles in development, fertility, and behavior [30]. Of especial importance to human health is the consistent finding that elevated E₂, often through hormone-replacement therapy, is associated with an increased risk of breast [31], endometrial [32], and ovarian [33] cancers. Also, in inseminated females, minute elevations in estrogen activity can impede blastocyst implantation, leading to pregnancy failure [30], [34]. Given the fact that triclosan exposure is ubiquitous, its potential capacity to modulate estrogen levels or activity in vivo is worthy of investigation. Here we investigated the impact of single or repeated triclosan injections on concentrations of exogenous tritium-labeled estradiol (³H-E₂) and endogenous urinary E₂. We hypothesized that a single injection of triclosan would elevate ³H-E₂ levels in reproductive tissues of cycling and peri-implantation female mice, and that this effect would be more pronounced with repeated triclosan injections over multiple days. We also hypothesized that triclosan administration would increase endogenous E₂ concentrations as measured in urine.