Metabonomics reveals that triclocarban affects liver metabolism by affecting glucose metabolism, β-oxidation of fatty acids, and the TCA cycle in male mice
Graphical abstract
Introduction
Triclocarban (TCC) is a broad-spectrum lipophilic antibacterial agent that is widely used in personal care products (Hinther et al., 2011; Halden, 2014; Wang et al., 2014). TCC is frequently used as a fungicide and preservative in detergents, cosmetics, medical disinfectants, air fresheners, fabric and leather finishing agents, deodorants, and other products because it has a high sterilization efficiency, is non-toxic, non-skin irritating, and non-allergenic, and has characteristics including good compatibility with skin as well as common raw materials in daily chemical products (Bester, 2003; Sabaliunas et al., 2003). Since its advent in 1957, TCC has been produced and used on a large scale, and its consumption in the United States reached 500 tons per year (Hinther et al., 2011; Halden, 2014), while its annual consumption in China has reached a peak of more than 1000 tons (Zhao et al., 2013). Its high consumption and stable physical and chemical properties (Schebb et al., 2011; Halden et al., 2005) make TCC one of the most commonly detected contaminants in the natural environment (Halden et al., 2005; Ying et al., 2007). The TCC concentration in sewage in North America, Europe, and Asia has reached μg/L levels (Halden et al., 2005; Ying et al., 2007), and it has been widely detected in major rivers in China—its concentration has been recorded up to 338 ng/L and 2723 ng/g in surface water and sediment, respectively (Zhao et al., 2013). Humans can be exposed to TCC via daily contact or diet because environmental TCC can be bio-absorbed through food chain enrichment (Coogan and Point, 2008; Coogan et al., 2007; Kennedy et al., 2015). The content of TCC in human urine was reported to reach 588 μg/L (Ye et al., 2016), and TCC is frequently detected in the urine and fingernail and toenail samples of the general Chinese population—0.40 μg/g creat, 95% CI 0.29–0.56; and 84.66 μg/kg and 41.50 μg/kg, respectively (Yin et al., 2016). Additionally, blood tests in pregnant women are used to detect fetal exposure to TCC (Wei et al., 2016).
Previous studies showed that TCC might act as an endocrine disruptor. For example, TCC regulates the activity of testosterone and estrogen, and the secretion of androgens in different animal models (Chen et al., 2008; Tsai et al., 2010; Duleba et al., 2011; Ahn et al., 2008; Chung et al., 2011; Hinther et al., 2011). TCC exposure might also result in an accumulation of its active compound epoxyeicosatrienoic acid (EET), which plays an important role in fatty acid metabolism in organisms, because TCC strongly inhibits soluble epoxide hydrolases (Liu et al., 2011). Studies have also revealed that TCC harms mammalian reproduction because castrated mice fed TCC-containing food showed greater testosterone activity and abnormally enlarged prostate glands and other male organs (Giudice and Young, 2010). Additionally, lactating mice exposed to TCC had offspring with a reduced survival rate (Kennedy et al., 2015). Other physiological abnormalities caused by TCC exposure include activated nuclear receptor constitutive androstane receptor (CAR) and CYP2b in a hUGT1ACar mouse model (Yueh et al., 2012), and DNA breakage and damage in a human hepatocyte (LO2) study caused by a low dose of TCC (2.38 μmol/L) (Li et al., 2010).
The liver is the most important organ for xenobiotic biotransformation, and is exposed to diffuse xenobiotics during its metabolic functions via cytochrome P450 and other enzymes (Spatzenegger and Jaeger, 1995; Gunegerieh, 1991). TCC is metabolized by CYP450 in rodents, monkeys, and humans (Hiles and Birch, 1978; Birch et al., 1978). There is experimental evidence suggesting that TCC affects lipid metabolism in offspring livers by perinatal exposure in CD-1 mice (Enright et al., 2017). However, the effect of TCC on liver metabolism in normal individuals has not been systematically studied, and the molecular mechanism involved in the effect on liver metabolism, especially for low-dose and short-term exposure, has not been examined.
To study the effect of TCC on liver metabolism and its molecular mechanism, TCC was orally administered by gavage to C57BL/6 mice for 35 days at a variety of doses, followed by a comparison of hepatic endogenous substances between TCC-treated and non-treated mice. We designed different exposure doses based on previous studies. The content of TCC in human urine reached 588 μg/L (Ye et al., 2016), and 27% of TCC was excreted through the urine when it was absorbed by the human body (Hiles and Birch, 1978). Overall exposure as high as 3.0 mg/kg per adult is possible because the urine volume in an adult is 1.4 L per day (Rose et al., 2015). Using an allometric scaling model (Reagan-Shaw et al., 2008), we determined the oral dose in mice was about 27.3 mg/kg. We focused on the systemic evaluation of alterations to hepatic endogenous substances after TCC exposure and determined the underlying metabolic pathway. We studied the correlation between key genes and metabolic pathways to verify and elucidate the mechanism of how TCC affects liver metabolism.
Section snippets
Chemicals
TCC was purchased from Sigma-Aldrich (St. Louis, MO, USA). The One-Step RNA PCR Kit was purchased from Takara (Dalian) Co. Ltd (Jilin, China). Mouse carnitine palmitoyl transferase-1 (CPT1) and acyl-CoA synthetase (ACS) were purchased from Shanghai Jianglai Biotechnology Co. Ltd (Shanghai, China). The fatty acid synthase (FAS)-linked immunoassay kit, acetyl coenzyme A carboxylase (ACC), citrate synthase (CS) kit, pyruvate dehydrogenase (PDH) kit, lactate dehydrogenase (LDH) kit, and
Effects of TCC exposure on the mouse liver visceral coefficient and pathology
Mice were treated with different doses of TCC once a day for 35 days. When the TCC dose reached or exceeded 10 mg/kg, the body weight, liver weight, and organ coefficient of treated mice changed significantly (Table 1). Similar changes were also observed for blood biochemical indicators, such as total protein (TP), glucose (GLU), alkaline phosphatase (ALP), and cholinesterase (CHE) (Table 2), but changes in other biochemical indexes were not obvious. This may be because the exposure time was
Conclusions
A high-resolution mass spectrometry-based metabonomic analysis was performed in this study, combined with a bioinformatics analysis, to determine the mechanism involved in the effect on liver metabolism. First, endogenous substances related to the effects of TCC on liver metabolism were detected by metabonomics; second, we demonstrated an intrinsic correlation between changes in metabolic pathways in the plasma and liver through a self-built metabolic pathway figure; and last, we used molecular
Conflict of interest
The authors declare they have no actual or potential competing financial interests.
Transparency document
Acknowledgments
This work was supported by grants from Basic Research Fund for Central Public Interest Institutes (No. 2017JK047; No. 2017JK009), The Natural Science Foundation of Beijing (No. 8164071), the Natural Science Foundation of China (No. 81273125 and 81373472), and the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) of the People’s Republic of China (No. 201510024 and 201510203-02).
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The first two authors contributed equally to this work.