An investigation of the role of microsomal oxidative metabolism in the in vivo genotoxicity of 1,2-dichloroethane

Involvement of CYP2E1 in the Course of Brain Edema Induced by Subacute Poisoning With 1,2-Dichloroethane in Mice

This study was designed to explore the role of cytochrome P4502E1 (CYP2E1) expression in the course of brain edema induced by subacute poisoning with 1,2-dichloroethane (1,2-DCE). Mice were randomly divided into five groups: the control group, the 1,2-DCE poisoned group, and the low-, medium- and high-dose diallyl sulfide (DAS) intervention groups. The present study found that CYP2E1 expression levels in the brains of the 1,2-DCE-poisoned group were upregulated transcriptionally; in contrast, the levels were suppressed by DAS pretreatment in the intervention groups. In addition, the expression levels of both Nrf2 and HO-1 were also upregulated transcriptionally in the brains of the 1,2-DCE-poisoned group, while they were suppressed dose-dependently in the intervention groups. Moreover, compared with the control group, MDA levels and water contents in the brains of the 1,2-DCE-poisoned group increased, whereas NPSH levels and tight junction (TJ) protein levels decreased significantly. Conversely, compared with the 1,2-DCE- poisoned group, MDA levels and water contents in the brains of the intervention groups decreased, and NPSH levels and TJ protein levels increased significantly. Furthermore, pathological changes of brain edema observed in the 1,2-DCE-poisoned group were markedly improved in the intervention groups. Collectively, our results suggested that CYP2E1 expression could be transcriptionally upregulated in 1,2-DCE-poisoned mice, which might enhance 1,2-DCE metabolism in vivo, and induce oxidative damage and TJ disruption in the brain, ultimately leading to brain edema.

Roles of CYP2e1 in 1,2-dichloroethane-induced liver damage in mice

The aim of this study was to explore the roles of cytochrome P450 2E1 (CYP2E1) in 1,2-dichloroethane (1,2-DCE)-induced liver damage. Two parts were included in this study: first, effect of 1,2-DCE on microsomal expression of CYP2E1, and second, potential of an inhibitor of CYP2E1 to reduce 1,2-DCE-induced liver damage. In part one, mice were exposed to 0, 0.225, 0.45, or 0.9 g/m³ 1,2-DCE for 10 days, 3.5 h per day through static inhalation. In part two, mice were divided into blank control, solvent control, inhibitor control, 1,2-DCE-poisoned group, and low or high intervention group. In part one, compared to the control, serum alanine aminotransferase (ALT) activities and hepatic malondialdehyde (MDA) levels in 0.9 g/m³ 1,2-DCE group, and microsomal CYP2E1 protein expression and activity in both 0.45 and 0.9 g/m³ 1,2-DCE groups increased significantly; conversely, hepatic nonprotein sulfhydryl (NPSH) levels in both 0.45 and 0.9 g/m³ 1,2-DCE groups and hepatic SOD activities in 0.9 g/m³ 1,2-DCE group decreased significantly. In part two, microsomal CYP2E1 protein expression and activity decreased significantly in both low and high intervention groups compared to 1,2-DCE-poisoned group. Along with the changes of CYP2E1, hepatic MDA levels and serum ALT activities decreased; conversely, hepatic NPSH levels and SOD activities increased significantly in high intervention group. Taken together, our results suggested that 1,2-DCE could enhance CYP2E1 protein expression and enzymatic activity, which could cause oxidative damage in liver, serving as an important mechanism underlying 1,2-DCE-induced liver damage. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1430-1438, 2016.

Alteration in mitochondrial function and glutamate metabolism affected by 2-chloroethanol in primary cultured astrocytes

The aim of this study was to explore the mechanisms that contribute to 1,2-dichloroethane (1,2-DCE) induced brain edema by focusing on alteration of mitochondrial function and glutamate metabolism in primary cultured astrocytes induced by 2-chloroethanol (2-CE), a metabolite of 1,2-DCE in vivo. The cells were exposed to different levels of 2-CE in the media for 24h. Mitochondrial function was evaluated by its membrane potential and intracellular contents of ATP, lactic acid and reactive oxygen species (ROS). Glutamate metabolism was indicated by expression of glutamine synthase (GS), glutamate-aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1) at both protein and gene levels. Compared to the control group, exposure to 2-CE could cause a dose dependent damage in astrocytes, indicated by decreased cell viability and morphological changes, and supported by decreased levels of nonprotein sulfhydryl (NPSH) and inhibited activities of Na⁺/K⁺-ATPase and Ca²⁺-ATPase in the cells. The present study also revealed both mitochondrial function and glutamate metabolism in astrocytes were significantly disturbed by 2-CE. Of which, mitochondrial function was much vulnerable to the effects of 2-CE. In conclusion, our findings suggested that mitochondrial dysfunction and glutamate metabolism disorder could contribute to 2-CE-induced cytotoxicity in astrocytes, which might be related to 1,2-DCE-induced brain edema.

1,2-Dichloroethane induced nephrotoxicity through ROS mediated apoptosis in vitro and in vivo

1,2-Dichloroethane (DCE) decreased kidney cell proliferation, even induced cell apoptosisviaincreasing the generation of ROS in the presence of an extra-metabolic system.

Acute toxicologic and neurotoxic effects of inhaled 1,2-dichloroethane in adult Fischer 344 rats

Acute toxicologic and neurotoxic effects were evaluated in Fischer 344 rats exposed to 0, 50, 200, 600, or 2000 ppm 1,2-dichloroethane (ethylene dichloride; EDC) for 4 h or 0, 50, 100 or 150 ppm for 8 h. Neurobehavioral and neuropathologic effects were assessed using a functional observational battery (FOB; baseline, days 1, 8, and 15), and by light microscopy, respectively. Acute toxicologic effects were assessed by bronchoalveolar lavage (BAL) and histopathology of the respiratory tract and selected target organs. Neurobehavioral effects consistent with central nervous system (CNS) depression were present at concentrations >200 ppm and were restricted to day 1. There were no neuropathologic changes in the CNS, however, olfactory epithelial regeneration 15 days after exposure to > or = 200 ppm was observed. The no-observed-effect concentration (NOEC) for behavioral neurotoxicity was 200 ppm EDC for 4 h. There were no effects on BAL parameters in any exposure group. Exposure to 2000 ppm EDC altered adrenal gland, kidney, and liver weights, and resulted in morphologic alterations in the kidney and liver. Degeneration/necrosis of the olfactory epithelium was observed at > or = 200 ppm for 4 h and > or = 100 ppm for 8 h. Based on olfactory epithelial degeneration/necrosis, the most sensitive indicator of toxicity in this study, the overall NOEC was 50 ppm EDC for up to 8 h in rats.

Assessment of cancer risk from ethylene oxide residues in spices imported into New Zealand

Quantitative estimates of cancer risks from ethylene oxide (ETO) residues were constructed based on 200 retail samples of various spices in New Zealand. Two samples of cinnamon contained detectable ETO. The highest value encountered was 15 ppm. ETO was not detected in the remaining 198 samples. However, 31 samples had detectable levels of ethylene chlorohydrin (ECH) and/or ethylene bromohydrin (EBH). A conservative estimate of ETO intake, based on average spice consumption, was 3.4 x 10(-6) mg/kg/day. Cancer potency factors for ETO ranging from 0.29 to 0.55 (mg/kg/day)(-1) were used to form cancer risk estimates. The resulting estimates of average lifetime excess cancer risk was 0.8 x 10(-6) to 1.7 x 10(-6). The US 97.5 percentile value for spice consumption (2.8 kg spices per year), gave an extreme upper-end estimate of lifetime cancer risk of approximately 1.4 x 10(-5). These risks are practically negligible considering the conservative assumptions used in estimating exposure to ETO. The exposures to ECH and EBH are 200-300-fold higher than to ETO. These compounds are of lesser potency to ETO in terms of mutagenicity or carcinogenicity in studies to date. However, the precise contribution of these compounds to the cancer risk estimate is uncertain due to large toxicological data gaps, including the absence of a 2-year cancer bioassay by the oral route.

Epithelial binding of 1,2-dichloroethane in mice

The metabolism and binding of 14C-labelled 1,2-dichloroethane (DCE) in female C57BL-mice were studied. As shown by whole-body autoradiography with heated and organic solvent-extracted tissue sections of i.v. injected mice, a selective localization of non-volatile and bound DCE-metabolites occurred in the nasal olfactory mucosa and the tracheo-bronchial epithelium. Low levels of metabolites were also present in the epithelia of the upper alimentary tract, vagina and eyelid, and in the liver and kidney. A decreased mucosal and epithelial binding was observed after pretreatment with metyrapone, indicating that the binding might be due to an oxidative metabolism of DCE. The quantitated levels of in vivo binding were considerably lower in mice injected i.p. with DCE, as compared to mice given equimolar doses of 14C-labelled 1,2-dibromoethane. In vitro experiments with 1000 g supernatants from various tissues showed that the nasal mucosa has a marked ability to activate DCE into products that become irreversibly bound to the tissue. It is proposed that the nasal olfactory mucosa is a target tissue for toxicity of DCE.

N-acetyl-S-(2-hydroxyethyl)-L-cysteine as a potential tool in biological monitoring studies? A critical evaluation of possibilities and limitations

In mammalian species, including man, N-acetyl-S-(2-hydroxyethyl)-L-cysteine (2-HEMA) is a common urinary metabolite of a large number of structurally different xenobiotic chemicals. It is a common urinary end product of glutathione pathway metabolism of a variety of chemicals possessing electrophilic properties and, in most cases, also a genotoxic potential. Five different chemically reactive intermediates, with different electrophilic properties, may be involved in the formation of 2-HEMA. An inventory of chemicals known to lead to the formation of 2-HEMA, or based on their chemical structure expected to do so, is presented. Furthermore, an attempt is made to evaluate the possibilities and limitations in terms of the potential use of urinary 2-HEMA as a tool in biomonitoring studies. Two other related, sulfur-containing urinary metabolites, i.e. N-acetyl-(S-carboxymethyl)-L-cysteine and thio-diacetic acid, are proposed as possible alternatives to urinary 2-HEMA. It is suggested that 2-HEMA might be seen as a potentially useful and sensitive signal parameter for the assessment of exposure of animals and man to a variety of electrophilic and therefore potentially toxic xenobiotic chemicals.

In vivo sister chromatid exchange induced by 1,2-dichloroethane on bone marrow cells of mice

In vivo sister chromatid exchange induced by 1,2-dichloroethane (DCE) was studied in bone marrow cells of mice after acute treatment for 24 hr. With the exception of the lowest concentration (0.5 mg/kg), each treated series exhibited a statistically significant increase in SCEs when compared with the control.

Interaction between 1,2-dichloroethane and tetraethylthiuram disulfide (disulfiram). II. Hepatotoxic manifestations with possible mechanism of action

The synergistic hepatotoxicity of dietary disulfiram (DSF) with 1,2-dichloroethane (DCE) subchronically administered by inhalation at three concentration levels (150, 300, and 450 ppm) was studied. The criteria for hepatotoxicity were treatment-related increases in serum activities of sorbitol dehydrogenase, 5'-nucleotidase, and alkaline phosphatase, and in liver-to-body weight ratios. DSF alone did not elicit these responses while DCE at the highest concentration level increased liver-to-body weight ratios and the activity of 5'-nucleotidase. Exposure to DSF alone decreased cytochrome P450 levels, but in combination with DCE, the decrement of cytochrome P450 was additive in a DCE concentration-dependent manner. However, depression of cytochrome P450 by DCE alone was not concentration dependent. Although DSF and DSF/DCE combination increased the activity of glutathione S-transferases (GSTs), both DSF and DCE singly and in combination increased the tissue levels of reduced glutathione (GSH). Evidence is presented showing that the potentiation of the hepatotoxicity of DCE observed in the presence of DSF may be due to an inhibition of microsomal mixed-function oxidase-mediated metabolism of DCE and to a compensatory increase in DCE metabolism to reactive metabolites generated by GST-mediated conjugation of DCE with GSH.