1,2-Dichloroethane impairs glucose and lipid homeostasis in the livers of NIH Swiss mice

doi:10.1016/j.tox.2017.02.005

Toxicology

Volume 380, 1 April 2017, Pages 38-49

https://doi.org/10.1016/j.tox.2017.02.005 Get rights and content

Highlights

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1,2-DCE exposure to mice induced mild hepatoxicity.
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1,2-DCE exposure led to mouse hepatic glycogen, FFA and triglyceride accumulation.
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1,2-DCE administration induced Akt1 phosphorylation level in mouse livers.
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1,2-DCE treatment resulted in decreases in hepatic G6PC and PYGL expression.
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The hepatic glycogen accumulation is mediated by 2-CA-induced Akt1activation.

Abstract

Excessive exposure to 1,2-Dichloroethane (1,2-DCE), a chlorinated organic toxicant, can lead to liver dysfunction. To fully explore the mechanism of 1,2-DCE-induced hepatic abnormalities, 30 male National Institutes of Health (NIH) Swiss mice were exposed to 0, 350, or 700 mg/m³ of 1,2-DCE, via inhalation, 6 h/day for 28 days. Increased liver/body weight ratios, as well as serum AST and serum ALT activity were observed in the 350 and 700 mg/m³ 1,2-DCE exposure group mice, compared with the control group mice. In addition, decreased body weights were observed in mice exposed to 700 mg/m³ 1,2-DCE, compared with control mice. Exposure to 350 and 700 mg/m³ 1,2-DCE also led to significant accumulation of hepatic glycogen, free fatty acids (FFA) and triglycerides, elevation of blood triglyceride and FFA levels, and decreases in blood glucose levels. Results from microarray analysis indicated that the decreases in glucose-6-phosphatase catalytic subunit (G6PC) and liver glycogen phosphorylase (PYGL) expression, mediated by the activation of AKT serine/threonine kinase 1 (Akt1), might be responsible for the hepatic glycogen accumulation and steatosis. Further in vitro study demonstrated that 2-chloroacetic acid (1,2-DCE metabolite), rather than 1,2-DCE, up-regulated Akt1 phosphorylation and suppressed G6PC and PYGL expression, resulting in hepatocellular glycogen accumulation. These results suggest that hepatic glucose and lipid homeostasis are impaired by 1,2-DCE exposure via down-regulation of PYGL and G6PC expression, which may be primarily mediated by the 2-chloroacetic acid-activated Akt1 pathway.

Introduction

1,2-Dichloroethane (1,2-DCE), commonly known as ethylene dichloride (EDC), is a type of halogenated aliphatic hydrocarbon. In industry, 1,2-DCE is primarily used as an intermediate to make vinyl chloride, trichloroethylene, and perchloroethylene. In China, it is extensively used as an organic solvent adhesive thinner. Furthermore, 1,2-DCE is also present in ambient air, groundwater, surface water, and drinking water (Chernichenko et al., 2009, Hou et al., 2012). It is a highly volatile liquid, thus the primary route of 1,2-DCE exposure for human beings is through vapor inhalation. After absorption, 1,2-DCE is quickly distributed and accumulates in organs rich in fat and lipids such as the brain, liver, kidney, spleen, and adipose tissue (Igwe et al., 1986, Take et al., 2014). During the past twenty years, 1,2-DCE poisoning has become one of the most severe occupational hazards in China (Liu et al., 2010, Chen et al., 2015a, Chen et al., 2015b; Zhou et al., 2015). According to reports, the concentration of 1,2-DCE in some workplaces can reach up to 500–1500 mg/m³ (123.52–370.57 ppm), which is much higher than the safety standard of 15 mg/m³ (about 3.71 ppm) set by the Chinese Labor and Hygiene Department.

Many studies have shown that the nervous system tissue is the main area for 1,2-DCE accumulation and can result in lethal toxic encephalopathy (Hotchkiss et al., 2010, Wang et al., 2014). However, inhalation of 1,2-DCE can also severely impair liver function, based on data from animal models and clinical investigations. For instance, 1,2-DCE inhalation has been shown to cause elevations in serum alanine aminotransferase (ALT) with hepatomegaly, steatosis, and biochemical abnormalities in the livers of mice (Storer et al., 1984, Sun et al., 2015). Results of a previous study in humans (Cheng et al., 1999) suggested that exposure to low or moderate levels of 1,2-DCE could result in a higher risk for developing hepatic damage in occupational workers compared with those not exposed to 1,2-DCE. In general, 1,2-DCE-induced liver abnormalities may involve necrosis (Storer et al., 1984), steatosis (Freundt et al., 1977), cirrhosis (Przezdziak and Bakula, 1975), and/or neoplasm (Nagano, 1998). One line of evidence has indicated that the accumulation of reactive oxygen species (ROS) (Sun et al., 2015), the impairment of macromolecules (Kitchin and Brown, 1994, Sasaki et al., 1998), and the dysfunction of the hepatocellular metabolism (Cottalasso et al., 1994a) might underlie the above hepatic toxic effects. Nevertheless, the molecular mechanism(s) responsible for the hepatic abnormalities induced by 1,2-DCE have yet to be clarified.

Section snippets

Chemicals and reagents

1,2-DCE, chloroethanol, chloroacetaldehyde, and 2-CA (chromatographic grade) were purchased from Guangzhou chemical reagent factory (Guangzhou, China). TaqMan^® Gene Expression Assays and 2 × TaqMan^® Gene Expression Master Mix were purchased from Applied Biosystems (Foster City, CA, USA). The primers used for mRNA qRT-PCR were purchased from Generay Biotechnology (Shanghai, China). The antibodies against mouse PYGL (1:1000), G6PC (1:1000), and β-actin (1:10,000) were purchased from Proteintech

Environmental parameters of the 1,2-DCE-inhalation exposure model

GC–MS results revealed that the actual levels of 1,2-DCE in the exposure chambers during the experiment were similar to the pre-designed 1,2-DCE concentrations. Additionally, other environmental exposure parameters were analogous in all groups, suggesting that the biological changes in mouse livers were mainly dependent on the doses of 1,2-DCE (Table 1).

The general toxic effects of 1,2-DCE in mouse livers

To validate the actual inhalable efficiency of 1,2-DCE, urine 1,2-DCE metabolites (2-chloroethanol, 2-chloroacetaldehyde, and 2-chloroacetic

Discussion

The mechanism of 1,2-DCE-induced hepatotoxicity has been attracting increasing interest from researchers. Several previous studies concerning 1,2-DCE hepatotoxicity focused on oxidative stress (Cottalasso et al., 1994b, Watanabe et al., 2007, Sun et al., 2015) and it has been suggested that the CYP2E1 pathway is involved in these processes. Although the current study found that 1,2-DCE exposure could induce CYP2E1 mRNA and protein expression in mouse livers, the increments in CYP2E1 expression

Conflict of interest statement

The authors declare that there are no conflicts of interest

Acknowledgements

This work was supported by the National Natural Science Foundations of China [grant number: 81273098, 81673140], the National Key Technology Research, Development Program of the Ministry of Science and Technology of China during the 12th Five-Year Plan Period [grant number: 2014BAI12B01], Natural Science Foundation of Guangdong Province [grant number: S2013010011816], the Guangzhou City Pearl River New Star of Science and Technology [grant number: 2013J2200020], Young teacher training Program

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¹: These authors contributed equally to this work.

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1,2-Dichloroethane impairs glucose and lipid homeostasis in the livers of NIH Swiss mice

Highlights

Abstract

Introduction

Section snippets

Chemicals and reagents

Environmental parameters of the 1,2-DCE-inhalation exposure model

The general toxic effects of 1,2-DCE in mouse livers

Discussion

Conflict of interest statement

Acknowledgements

Clin. Liver Dis.

J. Neurol. Sci.

Biochimie

Toxicology

Toxicol. Appl. Pharmacol.

Food Chem. Toxicol.

J. Environ. Sci. (China)

Toxicology

Toxicology

J. Neurol. Sci.

Front. Pharmacol.

Transplant. Proc.

J. Lipid Res.

Toxicol. Appl. Pharmacol.

Mutat. Res.

Cancer Lett.

BMC Genet.

Neurotoxicol. Teratol.

Enzymatic characterization of four new mutations in the glucose-6 phosphatase (G6PC) gene which cause glycogen storage disease type 1a

Ann. Hum. Genet.

Identification of a mutation in liver glycogen phosphorylase in glycogen storage disease type VI

Hum. Mol. Genet.