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Biotransformation of MTBE in mammals.
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Ethyl tert -butyl ether (ETBE) may be used in the future as an additive to gasoline to increase oxygen content and reduce tailpipe emissions of pollutants. Therefore, widespread human exposure may occur. To contribute to the characterization of potential adverse effects of ETBE, its biotransformation was compared in humans and rats after inhalation...
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Biotransformation can greatly influence the accumulation and, subsequently, toxicity of substances in living beings. Although traditionally these studies to quantify metabolization of a compound have been carried out with in vivo species, currently, in vitro test methods with very different cell lines are being developed for their evaluation. Howev...
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... TBA is further metabolized to 2-methyl-1,2-propanediol and 2-hydroxyisobutyrate. These metabolites are detected in rat and human urine (Amberg et al., 2000). Salazar et al. (2015) and Borghoff et al. (2017) independently developed rat ETBE PBK models, in which the mechanism of ETBE-induced tumorigenesis in the kidney and liver was elucidated by estimating the levels of its metabolite, TBA. ...
... The model of Salazar et al. proposed two metabolism pathways from ETBE to TBA, whereas the model of Borghoff et al. proposed a single oxidative metabolic pathway from ETBE to TBA. The latter model was validated by comparing estimated blood and urine ETBE levels and TBA urine levels during or after inhalation of ETBE with the rat exposure data (Amberg et al., 2000). In this model, obvious nonlinear kinetics due to metabolic saturation were predicted with inhalation of ETBA at 2000 ppm and higher concentrations. ...
... Blood levels of ETBE were measured approximately 20 times during this study. Amberg et al. (2000) also exposed three volunteers of each gender to 4.5-and 40.6-ppm ETBE in an exposure chamber for 4 hr. ...
Although physiologically based kinetic (PBK) modeling is informative for the risk assessment of industrial chemicals, chemical-specific input values for partition coefficients and metabolic parameters, including Vmax and Km are mostly unavailable; however, in silico methods, such as quantitative structure-property relationship (QSPR) could fill the absence. To assess the PBK model validity using necessary toxicokinetic (TK) parameters predicted by QSPR, the PBK model of ethyl tert-butyl ether (ETBE) as a model substance was constructed, in which the values of the partition coefficients, Vmax, and Km of ETBE were predicted using those of the related chemicals previously reported in the literature, and toxicokinetics of inhaled ETBE were stochastically estimated using the Monte Carlo simulation. The calculated ETBE concentrations in venous blood were comparable to the measured values in humans, implying that the reproducibility of ETBE toxicokinetics in humans was established in this PBK model. The Monte Carlo simulation was used to conduct uncertainty and sensitivity analyses of the dose metrics in terms of maximum blood concentration (Cmax) and area under the blood concentration-time curve (AUC) and the estimated Cmax and AUC were highly and moderately reliable, respectively. Conclusively, the PBK model validity combined with in silico methods of QSPR was demonstrated in an ETBE model substance. QSPR-PBK modeling coupled with the Monte Carlo simulation is effective for estimating chemical toxicokinetics for which input values are unavailable and for evaluating the estimation validity.
... Some studies (Amberg et al. 2000;Hong et al. 1999;EPA 2017) have identified TBA as one of the primary metabolites of MTBE and ETBE. Following an average of 90.1 mg/ m 3 and 757 mg/m 3 doses of MTBE, TBA was measured to have a half-life of 8.1 ± 2.0 h in the human urine. ...
Leaking underground storage tanks can contaminate the groundwater. Since the 1980s, California leaking underground storage tanks have released millions of gallons of petroleum containing tertiary butyl alcohol into the subsurface. This compound was banned in early 2000 due to human health concerns. The United States Environmental Protection Agency considers tertiary butyl alcohol an animal carcinogen and a potential human carcinogen. California has not established a maximum contaminant level for tertiary butyl alcohol. (1) Based on the documented health hazards, a maximum contaminant level should be developed for tertiary butyl alcohol in California. (2) The California Water Resources Control Board’s “Low Threat Closure Policy”, which is a tool to evaluate closure of leaking underground storage tank sites, does not require regulators to consider tertiary butyl alcohol contamination in soil or groundwater in their closure review. This practice should be revisited based upon tertiary butyl alcohol’s toxicity data, its biotransformation from methyl tertiary butyl ether, and its stability in the environment. This review summarizes toxicity, sources, and environmental transformation of tertiary butyl alcohol, aims to raise awareness regarding the magnitude of the tertiary butyl alcohol problem in groundwater, and urges California regulators to develop more stringent protocols for tertiary butyl alcohol treatment. The nine Regional Water Quality Control Boards regulate and oversee cleanup at leaking underground storage tank sites in California. This study will directly impact Regional Water Quality Control Boards regulatory practices and will help provide a framework for developing monitoring and cleanup strategy for tertiary butyl alcohol around the world.
... Based on these findings the following metabolic pathway was proposed. The ethers undergo oxidative dealkylation to form tert-butanol; tert-butanol can undergo conjugations plSSN: 1976-8257 eISSN: 2234-2753 reactions or be oxidized to 2-methyl-1,2-propanediol; the latter can be further oxidized to 2-hydroxyisobutyrate. Amberg and co-workers subsequently found that following exposure to MTBE or ETBE, 2-hydroxyisobutyrate was the major, and tert-butanol and 2-methyl-1,2-propane diol the minor urinary metabolites, both in rats and humans (44). These findings are consistent with those of Bernauer and co-workers (43) and indicate that the metabolic pathway in humans is the same as in rats. ...
Solvents can be used in the manufacture of medicinal products provided their residual levels in the final product comply with the acceptable limits based on safety data. At worldwide level, these limits are set by the “Guideline Q3C (R6) on impurities: guideline for residual solvents” issued by the ICH. Diisopropyl ether (DIPE) is a widely used solvent but the possibility of using it in the pharmaceutical manufacture is uncertain because the ICH Q3C guideline includes it in the group of solvents for which “no adequate toxicological data on which to base a Permitted Daily Exposure (PDE) was found”. We performed a risk assessment of DIPE based on available toxicological data, after carefully assessing their reliability using the Klimisch score approach. We found sufficiently reliable studies investigating subchronic, developmental, neurological toxicity and carcinogenicity in rats and genotoxicity in vitro. Recent studies also investigated a wide array of toxic effects of gasoline/DIPE mixtures as compared to gasoline alone, thus allowing identifying the effects of DIPE itself. These data allowed a comprehensive toxicological evaluation of DIPE. The main target organs of DIPE toxicity were liver and kidney. DIPE was not teratogen and had no genotoxic effects, either in vitro or in vivo. However, it appeared to increase the number of malignant tumors in rats. Therefore, DIPE could be considered as a non-genotoxic animal carcinogen and a PDE of 0.98 mg/day was calculated based on the lowest No Observed Effect Level (NOEL) value of 356 mg/m³ (corresponding to 49 mg/kg/day) for maternal toxicity in developmental rat toxicity study. In a worst-case scenario, using an exceedingly high daily dose of 10 g/day, allowed DIPE concentration in pharmaceutical substances would be 98 ppm, which is in the range of concentration limits for ICH Q3C guideline class 2 solvents. This result might be considered for regulatory decisions.
... For a 14 C-ETBE oral gavage study reported by JPEC (2008b), the model was able to predict the concentration of TBA in blood with time post-administration at either 400 or 5 mg kg À1 bw (Fig. 5A); however; the model over-predicted the cumulative TBA in the urine measured at 24 h post-administration at both dose levels (Fig. 5B). The model predicted urinary concentrations following inhalation exposure to 40 ppm ETBE (Amberg et al., 2000) (Fig. 6C), although the predictions of the TBA blood concentrations after inhalation exposure (Fig. 6B) were not as close to the observed data as for oral gavage (compare Fig. 5A). The ETBE blood concentrations were well-predicted for the 4 ppm ETBE exposure (Fig. 6A), but over-predicted for 40 ppm. ...
... exposures (Amberg et al., 2000). In another study in which rats were exposed by nose-only inhalation to 14 C-ETBE at 500, 1750 or 5000 ppm (Borghoff & Asgharian, 1996), the model simulated the increase in the percentage of dose exhaled and the decrease in the percentage of dose excreted in urine with increasing exposure concentrations for both male (Fig. 8C) and female (Fig. 8D) rats. ...
... ETBE blood concentration (A), TBA blood concentration (B), and cumulative amount of TBA in urine (C) of F344 rats exposed to 4 or 40 ppm (nominal concentrations) ETBE following a single 4 h inhalation exposure. Symbols represent mean ± SD of the actual data collected (Amberg et al., 2000; see Table 2 and Supporting information), with model simulations (lines) based on model parameter values provided in Table 3. ETBE, ethyl tertiary-butyl ether; TBA, tertiary-butyl alcohol. Figure 7. TBA blood concentration in male Sprague-Dawley rats orally administered 5 mg kg À1 bw day À1 14CETBE for 1 or 14 days. ...
In cancer bioassays, inhalation, but not drinking water exposure to ethyl tertiary-butyl ether (ETBE), caused liver tumors in male rats, while tertiary-butyl alcohol (TBA), an ETBE metabolite, caused kidney tumors in male rats following exposure via drinking water. To understand the contribution of ETBE and TBA kinetics under varying exposure scenarios to these tumor responses, a physiologically based pharmacokinetic model was developed based on a previously published model for methyl tertiary-butyl ether, a structurally similar chemical, and verified against the literature and study report data. The model included ETBE and TBA binding to the male rat-specific protein α2u–globulin, which plays a role in the ETBE and TBA kidney response observed in male rats. Metabolism of ETBE and TBA was described as a single, saturable pathway in the liver. The model predicted similar kidney AUC0–∞ for TBA for various exposure scenarios from ETBE and TBA cancer bioassays, supporting a male-rat-specific mode of action for TBA-induced kidney tumors. The model also predicted nonlinear kinetics at ETBE inhalation exposure concentrations above ~2000 ppm, based on blood AUC0–∞ for ETBE and TBA. The shift from linear to nonlinear kinetics at exposure concentrations below the concentration associated with liver tumors in rats (5000 ppm) suggests the mode of action for liver tumors operates under nonlinear kinetics following chronic exposure and is not relevant for assessing human risk. Copyright © 2016 The Authors Journal of Applied Toxicology Published by John Wiley & Sons Ltd
... Indeed, this alcohol is consumed by many youngsters without direct, severe and harmful to health consequences. Additionally, occupational exposure (vapors from fermentation vats in brewery or from gasoline) turned out to be of low risk as far as human intoxication is concerned (Amberg et al., 2000). In the light of the pharmacokinetics it should be mentioned that the metabolism of 2M2B in humans is much more intense and involves different pathways and metabolites in comparison with that in rats. ...
... What is more, the elimination follows first-order kinetics. Therefore, humans may respond differently than rats to the potential toxic effect of this alcohol (Amberg et al., 2000). Although this study indicated the low toxicity of 2M2B in human kidney cells, this experimental fact should not be regarded as an incentive for its illegal consumption. ...
... Two different methods were described to quantify TAA glucuronides. The first involved direct analysis of the glucuronides by GC/MS-determination of trimethylsilyl derivatives [3], but it was not very sensitive. A more sensitive method was using acid hydrolysis (10 M of sulfuric acid) of the glucuronides. ...
We presented a case of 28 year-old male, who was found in a deep coma complicated with acute respiratory failure because of recreational intoxication with tert-amyl alcohol (TAA). The TAA blood level at the admission was 83μg/mL determined by gas chromatography-mass spectrometry (GC-MS). In the last few months popularity of TAA among alcohol and drug addicted people in Europe is still growing. The main reasons of these are: self-healing of addiction, low price of this xenobiotic compare to alcohol, and problem to detect this xenobiotic in generally used screening tests.
... Metabolism of ETBE is similar in rats and humans (Miller et al., 1997;Amberg et al., 2000;McGregor, 2006McGregor, , 2007. After inhalation or ingestion, ETBE is promptly absorbed into the blood and rapidly distributed throughout the body. ...
... After inhalation or ingestion, ETBE is promptly absorbed into the blood and rapidly distributed throughout the body. ETBE is metabolized to tertiary-butyl alcohol (TBA) and acetaldehyde in the liver and TBA is further oxidized into 2-methyl-1,2-propanol and 2-hydroxyisobuteric acid and these metabolites are excreted into urine (Bernauer et al., 1998;Amberg et al., 1999Amberg et al., , 2000. Of these ETBE metabolites, acetaldehyde is a genotoxic in rodents, inducing gene mutation, sister chromatid exchanges, chromosomal aberrations and micronuclei in cultured mammalian cells and sister chromatid exchange in bone marrow cells of mice and hamsters administered acetaldehyde by intraperitoneal injection (IARC, 1999, Obe et al., 1979, Korte et al., 1981; IARC (IARC, 1999). ...
Ethyl tertiary-butyl ether (ETBE) is an oxygenated gasoline additive synthesized from ethanol and isobutene that is used to reduce CO2 emissions. To support the Kyoto Protocol, the production of ETBE has undergone a marked increase. Previous reports have indicated that exposure to ETBE or methyl tertiary-butyl ether resulted in liver and kidney tumors in rats and/or mice. These reports raise concern about the effects of human exposure being brought about by the increased use of ETBE. The present study was conducted to evaluate the genotoxicity of ETBE using micronucleus induction of polychromatic erythrocytes in the bone marrow of male and female rats treated with ETBE in the drinking-water at concentrations of 0, 1,600, 4,000 or 10,000 ppm or exposed to ETBE vapor at 0, 500, 1,500 or 5,000 ppm for 13 weeks. There were no significant increases in micronucleus induction in either the drinking water-administered or inhalation-administered groups at any concentration of ETBE; although, in both groups red blood cells and hemoglobin concentration were slightly reduced in the peripheral blood in rats administered the highest concentration of ETBE. In addition, two consecutive daily intraperitoneal injections of ETBE at doses of 0, 250, 500 or 1,000 mg/kg did not increase the frequency of micronucleated bone marrow cells in either sex; all rats receiving intraperitoneal injections of ETBE at a dose of 2,000 mg/kg died after treatment day 1. These data suggest that ETBE is not genotoxic in vivo.
... Sodium sulfate was added to the vials for salting out. For MPD analysis, samples were heated under hydrochloric acid at 90 @BULLET C for 30 min to transform dehydrate to iso-butylaldehyde (Amberg et al., 1999) and sodium chloride was used for the salting out in this assay. The area under the curve (AUC) of the blood AA, TBA and MPD concentrations were calculated by the trapezoidal method from the exposure start to 24 h after exposure. ...
Ethyl tertiary butyl ether (ETBE) is biofuel additive recently used in Japan and some other countries. Limited evidence shows that ETBE has low toxicity. Acetaldehyde (AA), however, as one primary metabolite of ETBE, is clearly genotoxic and has been considered to be a potential carcinogen. The aim of this study was to evaluate the effects of ALDH2 gene on ETBE-induced genotoxicity and metabolism of its metabolites after inhalation exposure to ETBE. A group of wild-type (WT) and Aldh2 knockout (KO) C57BL/6 mice were exposed to 500ppm ETBE for 1- 6h, and the blood concentrations of ETBE metabolites, including AA, tert-butyl alcohol and 2-methyl-1,2-propanediol, were measured. Another group of mice of WT and KO were exposed to 0, 500, 1750, or 5000ppm ETBE for 6h/day with 5 days per weeks for 13 weeks. Genotoxic effects of ETBE in these mice were measured by the alkaline comet assay, 8-hydroxyguanine DNA-glycosylase modified comet assay and micronucleus test. With short-term exposure to ETBE, the blood concentrations of all the three metabolites in KO mice were significantly higher than the corresponding concentrations of those in WT mice of both sexes. After subchronic exposure to ETBE, there was significant increase in DNA damage in a dose-dependent manner in KO male mice, while only 5000ppm exposure significantly increased DNA damage in male WT mice. Overall, there was a significant sex difference in genetic damage in both genetic types of mice. These results showed that ALDH2 is involved in the detoxification of ETBE and lack of enzyme activity may greatly increase the sensitivity to the genotoxic effects of ETBE, and male mice were more sensitive than females.
... However, MTBE, which is most widely used oxygenate, has been considered to be an animal carcinogen, e.g., it may induce the renal tubular tumors in male Fischer 344 rats (Bird et al. 1997) and hepatic neoplasms in CD-1 mice (Burleigh-Flayer et al. 1992). Because chemical structure and biotransformation of ETBE appears to be similar to that of MTBE (Amberg et al. 2000), it is expected that the toxicity of ETBE should be similar to that of MTBE. By the histopathological assessments in this study, we observed that centrilobular hypertrophy in the livers of WT and KO mice of both sexes exposed to 5,000 ppm ETBE. ...
... AA is a known carcinogen (Baan et al. 2007) and has been proven to cause a variety of DNA damage, such as point mutations, sister chromatid exchanges, DNA strand breaks, oxidative base modiWcations, and gross chromosomal aberrations (Seitz and Stickel 2007). In addition, toxicokinetic studies demonstrated that ETBE in blood is rapidly metabolized or eliminated (Amberg et al. 2000). Taken together, it suggests that AA might be the major metabolite responsible for the genetic eVects after exposure to ETBE. ...
... # P < 0.05; ## P < 0.01; ### P < 0.001, as compared with control group of KO mice (Dunnett's post hoc test) mice are more sensitive to ETBE and its metabolitesinduced toxicity than female mice. However, study on the pharmacokinetics of ETBE showed no signiWcant sex diVerences in biotransformation in either species (Amberg et al. 2000). Interestingly, many reports demonstrated that TBA as a common metabolite of ETBE and MTBE could increase incidences of kidney tumors in male rats (Cirvello et al. 1995;Bird et al. 1997) mediated through an alpha-2 mu-globulin mechanism which is involved in non-genotoxic mode of action to induce tumors in rodents (Swenberg and Lehman-McKeeman 1999), and alpha-2 mu-globulin is a speciWc male rat protein, absent in humans. ...
Ethyl tertiary butyl ether (ETBE) is used as an additive to gasoline to reduce carbon monoxide emissions in some developed countries. So far, ETBE was not found with positive results in many genotoxic assays. This study is undertaken to investigate the modifying effects of deficiency of aldehyde dehydrogenase 2 (ALDH2) on the toxicity of ETBE in the livers of mice. Eight-week-old wild-type (WT) and Aldh2 knockout (KO) C57BL/6 mice of both sexes were exposed to 0, 500, 1,750, and 5,000 ppm ETBE for 6 h/day with 5 days per weeks for 13 weeks. Histopathology assessments and measurements of genetic effects in the livers were performed. Significantly increased accidences of centrilobular hypertrophy were observed in the livers of WT and KO mice of both sexes in 5,000 ppm group; there was a sex difference in centrilobular hypertrophy between male and female KO mice, with more severe damage in the males. In addition, DNA strand breaks, 8-hydroxyguanine DNA-glycosylase (hOGG1)-modified oxidative base modification, and 8-hydroxydeoxyguanosine as genetic damage endpoints were significantly increased in three exposure groups in KO male mice, while these genotoxic effects were only found in 5,000 ppm group of KO female mice. In WT mice, significant DNA damage was seen in 5,000 ppm group of male mice, but not in females. Thus, sex differences in DNA damage were found not only in KO mice, but also in WT mice. These results suggest that ALDH2 polymorphisms and sex should be taken into considerations in predicting human health effects of ETBE exposure.
... t-Butanol (TBA) is the primary metabolite of ETBE (18). Although Yamaki and Yoshino (11) found that TBA inhibited degranulation in a rat mast cell line, RBL2H3, there has been no report on the effect of TBA on splenocytes and other immune functions. ...
Ethyl tertiary-butyl ether (ETBE) is a motor fuel oxygenate used in reformulated gasoline. The current use of ETBE in gasoline or petrol is modest but increasing. To investigate the effects of ETBE on splenocytes, mice were exposed to 0 (control), 500 ppm, 1750 ppm, or 5000 ppm of ETBE by inhalation for 6 h/day for 5 days/wk over a 6- or 13-week period. Splenocytes were harvested from the control and exposed mice, and the following cell phenotypes were quantified by flow cytometry: (1) B cells (PerCP-Cy5.5-CD45R/B220), (2) T cells (PerCP-Cy5-CD3e), (3) T cell subsets (FITC-CD4 and PE-CD8a), (4) natural killer (NK) cells (PE-NK1.1), and (5) macrophages (FITC-CD11b). Body weight and the weight of the spleen were also examined. ETBE-exposure did not affect the weight of the spleen or body weight, while it transiently increased the number of RBC and the Hb concentration. The numbers of splenic CD3+, CD4+, and CD8+ T cells, the percentage of CD4+ T cells and the CD4+/CD8+ T cell ratio in the ETBE-exposed groups were significantly decreased in a dose-dependent manner. However, ETBE exposure did not affect the numbers of splenic NK cells, B cells, or macrophages or the total number of splenocytes. The above findings indicate that ETBE selectively affects the number of splenic T cells in mice.
