Hepatotoxic effect of 1-bromopropane and its conjugation with glutathione in male ICR mice

Diurnal variability in urinary volatile organic compound metabolites and its association with oxidative stress biomarkers

Volatile organic compounds (VOCs) are ubiquitous environmental pollutants that are associated with birth defects, leukemia, neurocognitive deficits, reproductive impairment and cancer in humans exposed to these compounds. Exposure to VOCs can be assessed by measuring their metabolites in urine. Little is known, however, about the temporal variability in urinary VOC metabolite (VOCM) concentrations within- and between-individuals. In this study, we determined the variability in the concentrations of 38 VOCMs in urine samples collected from 19 healthy individuals across a period of 44 days. We also measured seven biomarkers of oxidative stress (lipid, protein and DNA damage) in urine to assess the relationship of VOC exposure to oxidative stress. Seventeen VOCMs had detection frequencies (DFs) of >60% in urine, and we limited further data analysis to those compounds. The creatinine-adjusted geometric mean concentrations of VOCMs ranged from 2.70 μg/g to 327 μg/g in spot and 2.60 μg/g to 551 μg/g in first morning void (FMV) urine samples. Calculation of the intra-class correlation coefficients (ICCs) for 17 VOCM concentrations to assess their predictability and repeatability in urinary measurements showed ranges of 0.080-0.425 in spot and 0.050-0.749 in FMV urine samples, revealing notable within-individual variability. Our results suggest that taking only single measurements of VOCM concentrations in urine in epidemiological investigations may lead to exposure misclassification. In addition, VOCM concentrations were significantly and positively correlated with oxidative stress biomarkers. This study thus provides important information for formulating sampling strategies in the biomonitoring of VOC exposure in human populations.

Identification of DNA and glutathione adducts in male Sprague-Dawley rats exposed to 1-bromopropane

Occupational exposure of workers to 1-bromopropane (1-BP) has raised concerns in industry for many years. Despite the known toxicity of this chemical, molecular events attributed to exposure to 1-BP have not been extensively studied. The aim of the present study was to examine the effects of 1-BP exposure on adduct formation with DNA and glutathione (GSH) in male Sprague-Dawley rats in an attempt to determine the early stages of toxicity. Following 6 h after either single or daily exposure to 1-BP for 3 days, N⁷-propyl guanine and S-propyl GSH were quantified in several organs by using liquid chromatography-mass spectrometry (LC-MS/MS). The results showed that N⁷-propyl guanine was maximally formed in liver followed by spleen, testes, and lung in both dose- and time-dependent manners. However, DNA adduct was not detected in cardiac tissue. In the case of S-propyl GSH, this compound was formed in the following order in various organs: liver > testes > spleen > kidney > lung > heart. In a subsequent in vitro study, formation of N⁷-propyl guanine initiated by 1-BP in calf thymus DNA was not markedly affected by addition of liver homogenates, which indicated that this chemical may be acting as a direct alkylating agent. In contrast, an in vitro study with free GSH demonstrated that 1-BP reduced GSH and elevated production of S-propyl GSH, and that the production of this adduct was significantly higher in the presence of active liver homogenates. Data indicated that formation of GSH adducts initiated by 1-BP might be associated with an enzyme-driven process. Although further characterization is necessary, it would appear that N⁷-propyl guanine and S-propyl GSH might serve as useful markers in cases of exposure assessment of 1-BP.

Effect of 4-week inhalation exposure to 1-bromopropane on blood pressure in rats

The pathophysiology of hypertension is complex and multifactorial, and includes exposure to various chemical substances. Several recent studies have documented the reproductive and neurological toxicities of 1-bromopropane (1-BP). Given that 1-BP increased reactive oxygen species in the brain of rats, we hypothesized that 1-BP also has cardiovascular toxicity through increased oxidative stress. To test this hypothesis, male F344 and Wistar Nagoya rats (n = 7-8 per group per test) were exposed to 0 or 1000 ppm of 1-BP via inhalation for 4 weeks (8 h per day, 7 days per week). The exposure to 1-BP increased systolic blood pressure. This effect was associated with a significant decrease in the reduced/oxidized glutathione ratio. A significant increase in nitrotyrosine levels, activation of the NADPH oxidase pathway, which was evidenced by upregulation of gp91phox, a NADPH oxidase subunit, and significant decreases in the expressions of antioxidant molecules such as Cu/Zn- and Mn-superoxide dismutase catalase, and nuclear factor erythroid 2-related factor 2, were observed in the aortas of Wistar Nagoya rats exposed to 1-BP. Our results indicate that subacute (4-week) inhalation exposure to 1-BP increases blood pressure and suggest that this cardiovascular toxic effect is due, at least in part, to increased oxidative stress mediated through activation of the NADPH oxidase pathway. Further study is needed to assess whether NADPH oxidase activation causes the increase in blood pressure in the rats exposed to 1-BP. Copyright © 2016 John Wiley & Sons, Ltd.

Role of the Nrf2-ARE pathway in liver diseases

The liver is a central organ that performs a wide range of functions such as detoxification and metabolic homeostasis. Since it is a metabolically active organ, liver is particularly susceptible to oxidative stress. It is well documented that liver diseases including hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma are highly associated with antioxidant capacity. NF-E2-related factor-2 (Nrf2) is an essential transcription factor that regulates an array of detoxifying and antioxidant defense genes expression in the liver. It is activated in response to electrophiles and induces its target genes by binding to the antioxidant response element (ARE). Therefore, the roles of the Nrf2-ARE pathway in liver diseases have been extensively investigated. Studies from several animal models suggest that the Nrf2-ARE pathway collectively exhibits diverse biological functions against viral hepatitis, alcoholic and nonalcoholic liver disease, fibrosis, and cancer via target gene expression. In this review, we will discuss the role of the Nrf2-ARE pathway in liver pathophysiology and the potential application of Nrf2 as a therapeutic target to prevent and treat liver diseases.

Elevation of 4-hydroxynonenal and malondialdehyde modified protein levels in cerebral cortex with cognitive dysfunction in rats exposed to 1-bromopropane

1-Bromopropane (1-BP), an alternative to ozone-depleting solvents (ODS), exhibits central nervous system (CNS) toxicity in animals and humans. This study was designed to relate CNS damage by Morris water maze (MWM) test and oxidative stress to 1-BP exposure in the rat. Male Wistar rats were randomly divided into 4 groups (n=10), and treated with 0, 200, 400 and 800 mg/kgbw 1-BP for consecutive 12 days, respectively. From day 8 to day 12 of the experiment, MWM test was employed to assess the cognitive function of rats. The cerebral cortex of rats was obtained immediately following the 24h after MWM test conclusion. Glutathione (GSH), oxidized glutathione (GSSG) and total thiol (total-SH) content, GSH reductase (GR) and GSH peroxidase (GSH-Px) activities, malondialdehyde (MDA) level, as well as 4-hydroxynonenal (4-HNE) and MDA modified proteins in homogenates of cerebral cortex were measured. The obtained results showed that 1-BP led to cognitive dysfunction of rats, which was evidenced by delayed escape latency time and swimming distances in MWM performance. GSH and total-SH content, GSH/GSSG ratio, GR activity significantly decreased in cerebral cortex of rats, coupling with the increase of MDA level. 4-HNE and MDA modified protein levels obviously elevated after 1-BP exposure. GSH-Px activities in cerebral cortex of rats also increased. These data suggested that 1-BP resulted in enhanced lipid peroxidation of brain, which might play an important role in CNS damage induced by 1-BP.

In vitro human epidermal penetration of 1-bromopropane

1-Bromopropane (1-BP; CAS number 106-94-5), also known as n-propyl bromide, is a halogenated short-chain alkane used as an organic solvent with numerous commercial and industrial applications, including garment dry cleaning and vapor degreasing of metals. The purpose of this study was to determine the dermal absorption characteristics and corrosivity of 1-BP. Heat-separated human epidermal membranes were mounted on static diffusion cells. Different exposure scenarios were studied (infinite dose, finite dose, and transient exposure) using neat 1-BP and saturated aqueous solution as donor. Steady-state fluxes for infinite-dose neat 1-BP exposure averaged 625 to 960 μg cm(-2) h(-1). The finite-dose (10 μl/cm(2) = 13.5 mg/cm(2)) unoccluded donor resulted in penetration of <0.2% of the applied dose (22 μg/cm(2)). A 10-min transient exposure to infinite dose resulted in total penetration of 179 μg/cm(2). Steady-state 1-BP fluxes from neat application of a commercial dry cleaning solvent were similar (441 to 722 μg cm(-2) h(-1)). The permeability coefficient of 1-BP in water vehicle was 0.257 ± 0.141 cm/h. The absorption potential of 1-BP following dermal exposure is dependent upon the type and duration of exposure. Donor losses due to evaporation were approximately 500-fold greater than dermal absorption flux; evaporation flux was 420 mg cm(-2) h(-1). 1-BP is cytotoxic but not corrosive, based on results from a cultured reconstructed human epidermal model (EpiDerm Skin Corrosivity Test).

Role of Glutathione Conjugation in 1-Bromobutane-induced Immunotoxicity in Mice

Halogenated organic compounds, such as 1-bromobutane (1-BB) , have been used as cleaning agents, agents for chemical syntheses or extraction solvents in workplace. In the present study, immunotoxic effects of 1-BB and its conjugation with glutathione (GSH) were investigated in female BALB/c mice. Animals were treated orally with 1-BB at 375, 750 and 1500 mg/kg in corn oil once for dose response or treated orally with 1-BB at 1500 mg/kg for 6, 12, 24 and 48 hr for time course. S-Butyl GSH was identified in spleen by liquid chromatography-electrospray ionization tandem mass spectrometry. Splenic GSH levels were significantly reduced by single treatment with 1-BB. S-Butyl GSH conjugates were detected in spleen from 6 hr after treatment. Oral 1-BB significantly suppressed the antibody response to a T-dependent antigen and the production of splenic intracellular interlukin-2 in response to Con A. Our present results suggest that 1-BB could cause immunotoxicity as well as reduction of splenic GSH content, due to the formation of GSH conjugates in mice. The present results would be useful to understand molecular toxic mechanism of low molecular weight haloalkanes and to develop biological markers for exposure to haloalkanes.

Increased susceptibility of Nrf2-null mice to 1-bromopropane-induced hepatotoxicity

1-Bromopropane (1-BP) was introduced as an alternative to ozone-depleting solvents. However, it was found to exhibit neurotoxicity, reproductive toxicity, and hepatotoxicity in rodents and neurotoxicity in human. However, the mechanisms underlying the toxicities of 1-BP remain elusive. The present study investigated the role of oxidative stress in 1-BP-induced hepatotoxicity using nuclear factor erythroid 2-related factor 2 (Nrf2)-null mice. Groups of 24 male Nrf2-null mice and 24 male wild-type (WT) C57BL/6J mice were each divided into three groups of eight and exposed to 1-BP at 0, 100, or 300 ppm for 8 h/day for 28 days by inhalation. Liver histopathology showed significantly larger area of necrosis in Nrf2-null mice relative to WT mice at the same exposure level. Nrf2-null mice also had greater malondialdehyde (MDA) levels, higher ratio of oxidized glutathione/reduced form of glutathione, and lower total glutathione content. The constitutive level and the increase in ratio per exposure level of glutathione S-transferase (GST) activity were lower in the liver of Nrf2-null mice than WT mice. Exposure to 1-BP at 300 ppm increased the messenger RNA levels of heme oxygenase-1 (HO-1), glutamate-cysteine ligase modifier subunit (GcLm), glutamate-cysteine synthetase (GcLc), glutathione reductase, and NAD(P)H: quinone oxidoreductase 1 (NQO1) in WT mice but not in Nrf2-null mice except for GST Yc2. Nrf2-null mice were more susceptible to 1-BP-induced hepatotoxicity. That oxidative stress plays a role in 1-BP hepatotoxicity is deduced from the low expression levels and activities of antioxidant enzymes and high MDA levels in Nrf2-null mice.

Role of metabolism in 1-bromopropane-induced hepatotoxicity in mice

A possible role of metabolism in 1-bromopropane (1-BP)-induced hepatotoxicity was investigated in male ICR mice. The depletion of glutathione (GSH) by formation of GSH conjugates was associated with increased hepatotoxicity in 1-BP-treated mice. The formation of S-propyl and 2-hydroxypropyl GSH conjugates were identified in the liver following 1-BP treatment. In addition, the formation of reactive metabolites of 1-BP by certain cytochrome P-450 (CYP) may be involved in 1-BP-induced hepatotoxicity. The decreased content of hepatic GSH produced by 1-BP was associated not only with increased activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) but also with elevated levels of hepatic thiobarbituric acid-reactive substance (TBARS) in mice where metabolic enzymes were induced by pretreatment with phenobarbital. In addition, the hepatotoxicity induced by 1-BP was prevented by pretreatment with SKF-525A. Taken together, the formation of reactive metabolites by CYP and depletion of GSH may play important roles in hepatotoxicity induced by 1-BP.

Comparative study on susceptibility to 1-bromopropane in three mice strains

Previous studies indicate that 1-bromopropane (1BP) has neurotoxicity and reproductive toxicity both in humans and animals. The present study investigated strain differences in susceptibility to 1BP and identified possible biological factors that determine such susceptibility. Twenty-four male mice of each of the three strains (C57BL/6J, DBA/2J, and BALB/cA) were divided into four groups of six each and exposed to 1BP at 0, 50, 110, and 250 ppm for 8 h/day for 28 days by inhalation. At the end of exposure period, the relative susceptibilities of each strain to 1BP-mediated hepatotoxicity and male reproductive toxicity were evaluated. The contributing factors to strain-dependent susceptibility were assessed by determination of hepatic CYP2E1 levels, glutathione-S-transferase (GST) activity, glutathione (GSH) status, and NAD(P)H:quinone oxidoreductase and heme oxygenase-1 mRNA levels. Liver histopathology showed significantly larger area of liver necrosis and more degenerative lobules in BALB/cA in the order of BALB/cA > C57BL/6J > DBA/2J. BALB/cA showed higher CYP2E1 protein level and lower total GSH content and GST activity in the liver than DBA/2J. These results indicate that BALB/cA mice are the most susceptible to hepatotoxicity of 1BP among the three strains tested, and that CYP2E1, GSH level/GST activity may contribute to the susceptibility to 1BP hepatotoxicity. Exposure to > or = 50 ppm of 1BP also decreased sperm count and sperm motility and increased sperms with abnormal heads in all three strains mice in a dose-dependent manner. Comparison with previous studies in rats indicates that mice are far more susceptible than rats to 1BP regarding hepatotoxicity and reproductive toxicity.

Hepatotoxic and immunotoxic effects produced by 1,3-dibromopropane and its conjugation with glutathione in female BALB/c mice

To determine a possible role of glutathione (GSH) conjugation in 1,3-dibromopropane (1,3-DBP)-induced hepatotoxicity and immunotoxicity, female BALB/c mice were treated orally with 1,3-DBP. Based on the liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS) analyses, two forms of S-bromopropyl GSH were observed at m/z 427.9 and 429.9 in the positive ESI spectrum with a retention time of 5.29 and 5.23 min, respectively. Following single treatment of mice with 150, 300 or 600 mg/kg 1,3-DBP for 12 hr, the amount of S-bromopropyl GSH was detected maximally in liver homogenates at 600 mg/kg 1,3-DBP. Hepatic GSH levels were significantly decreased by treatment with 1,3-DBP. In a time course study, production of S-bromopropyl GSH rose maximally 6 hr after treatment and decreased gradually thereafter. The liver weights were significantly increased by treatment with 600 mg/kg 1,3-DBP. When mice were treated orally with 600 mg/kg 1,3-DBP for 12 hr, the activities of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were increased by 365- and 83-fold. In addition, oral 1,3-DBP significantly suppressed the antibody response to a T-dependent antigen at 600 mg/kg 1,3-DBP. 1,3-DBP elevated hepatic levels of malondialdehyde and suppressed the activities of some hepatic enzymes involved in anti-oxidation. Taken together, the formation of GSH conjugate with 1,3-DBP may deplete cellular GSH and, subsequently, produce hepatotoxicity and immunotoxicity via damage to the cellular anti-oxidative system.

CYP2E1-Catalyzed Oxidation Contributes to the Sperm Toxicity of 1-Bromopropane in Mice1

1-bromopropane (1-BrP) induces dose- and time-dependent reproductive organ toxicity and reduced sperm motility in rodents. The contribution of cytochrome P4502E1 (CYP2E1) to both 1-BrP metabolism and the induction of male reproductive toxicity was investigated using wild-type (WT) and Cyp2e1-/- mice. In gas uptake inhalation studies, the elimination half-life of [1,2,3-(13)C]-1-BrP was longer in Cyp2e1-/- mice relative to WT (3.2 vs. 1.3 h). Urinary metabolites were identified by 13C nuclear magnetic resonance. The mercapturic acid of 1-bromo-2-hydroxypropane (2OHBrP) was the major urinary metabolite in WT mice, and products of conjugation of 1-BrP with glutathione (GSH) were insignificant. The ratio of GSH conjugation to 2-hydroxylation increased 5-fold in Cyp2e1-/- mice relative to WT. After 1-BrP exposure, hepatic GSH was decreased by 76% in WT mice vs. 47% in Cyp2e1-/- mice. Despite a 170% increase in 1-BrP exposure in Cyp2e1-/- vs. WT mice, sperm motility in exposed Cyp2e1-/- mice did not change relative to unexposed matched controls. This suggests that metabolites produced through CYP2E1-mediated oxidation may be responsible for 1-BrP-induced sperm toxicity. Both 1-BrP and 2OHBrP inhibited the motility of sperm obtained from WT mice in vitro. However, only 2OHBrP reduced the motility of sperm obtained from Cyp2e1-/- mice in vitro, suggesting that conversion of parent compound to 2OHBrP within the spermatozoa may contribute, at least in part, to reduced motility. Overall, these data suggest that metabolism of 1-BrP is mediated in part by CYP2E1, and activation of 1BrP via this enzyme may contribute to the male reproductive toxicity of this chemical.

Role of glutathione conjugation in the hepatotoxicity and immunotoxicity induced by 1-bromopropane in female BALB/c mice

1-Bromopropane (1-BP) is used as a cleaning agent or adhesive solvent in the workplace. In the present study, the hepatotoxic and immunotoxic effects of 1-bromopropane and its conjugation with glutathione (GSH) were investigated in female BALB/c mice. The animals were treated orally with 200, 500 and 1000 mg kg(-1) of 1-BP in corn oil for a dose response study or treated orally with 1000 mg kg(-1) of 1-BP for 6, 12, 24 and 48 h for a time course study. The hepatic and splenic contents of GSH were significantly decreased by 1-BP in a dose-dependent manner. S-propyl GSH was identified in livers following treatment with 1-BP by liquid chromatography-electrospray ionization tandem mass spectrometry. When the production of conjugates from 1-BP was investigated in livers following oral treatment with 1000 mg kg(-1) of 1-BP for 6, 12, 24 and 48 h, the GSH conjugates were detected maximally 6 h after treatment. Treatment of mice with 1-BP increased the serum activity of alanine aminotransferase dose-dependently. The oral 1-BP treatment significantly suppressed the antibody response to a T-dependent antigen and the production of splenic intracellular IL-2 in response to Con A in a dose-dependent manner. The present results suggested that 1-BP could cause hepatotoxicity and immunotoxicity as well as depletion of GSH content due to the formation of GSH conjugates.