Ethyl tertiary-butyl ether: a toxicological review

Investigation of the potential mutagenicity of ethyl tertiary-butyl ether in the tumor target tissue using transgenic Big Blue Fischer 344 rats following whole body inhalation exposure

Ethyl tertiary-butyl ether (ETBE) is a fuel oxygenate used for the efficiency of motor vehicle fuels and their octane ratings. ETBE has been reported to induce liver adenomas in male rats in a 2-year bioassay at the highest inhalation concentration tested of 5000 ppm. To investigate the potential mutagenicity of ETBE in the liver, male Big Blue Fischer 344 rats were exposed for 28 consecutive days (6 h/day) to 0, 500, 1500, and 5000 ppm ETBE. The treated rats were sacrificed 3 days post-exposure and the frequencies of cII mutants were evaluated in the liver and bone marrow tissues. The mutant frequency (MF) of the liver in the negative control group was 36.3 × 10^-6 and this value was not significantly different in ETBE-exposed animals (39.4, 37.3, and 45.9 × 10^-6 in 500, 1500, and 5000 ppm groups, respectively). In the bone marrow, the mean MF in the negative control was 32.9 × 10^-6 which was not different from the means of the exposed groups (33.8, 22.6, and 32.0 × 10^-6 for groups exposed to 500, 1500 and 5000 ppm, respectively). These data, along with consistent negative response reported in the literature for other apical genotoxicity endpoints informs that mutagenicity is not likely the initial key event in the mode of action for ETBE-induced hepatocarcinogenesis in the rat.

Comparative Proteomic Analysis of an Ethyl Tert-Butyl Ether-Degrading Bacterial Consortium

A bacterial consortium capable of degrading ethyl tert-butyl ether (ETBE) as a sole carbon source was enriched and isolated from gasoline-contaminated water. Arthrobacter sp., Herbaspirillum sp., Pseudacidovorax sp., Pseudomonas sp., and Xanthomonas sp. were identified as the initial populations with the 16S rDNA analysis. The consortium aerobically degraded 49% of 50 mg/L of ETBE, in 6 days. The ETBE degrading efficiency of the consortium increased to 98% even with the higher concentrations of ETBE (1000 mg/L) in the subsequent subcultures, which accumulated tert-butyl alcohol (TBA). Xanthomonas sp. and Pseudomonas sp. were identified as the predominant ETBE degrading populations in the final subculture. The metaproteome of the ETBE-grown bacterial consortium was compared with the glucose-grown bacterial consortium, using 2D-DIGE. Proteins related to the ETBE metabolism, stress response, carbon metabolism and chaperones were found to be abundant in the presence of ETBE while proteins related to cell division were less abundant. The metaproteomic study revealed that the ETBE does have an effect on the metabolism of the bacterial consortium. It also enabled us to understand the responses of the complex bacterial consortium to ETBE, thus revealing interesting facts about the ETBE degrading bacterial community.

Migration of Volatile Organic Compounds (VOCs) from PEX-a Pipes into the Drinking Water during the First Five Years of Use

A brand-new office building in Rauma, Finland, was used to study the first five years of PEX-a drinking water pipes in normal use. Both pipe material and water samples from hot and cold-water pipelines were analyzed. Migration of volatile organic compounds (VOC) from the PEX-a pipes into the drinking water was observed to decrease rapidly during the first months. Deterioration of the PEX-a material was observed to take place due to the wearing down of organic antioxidants added into the PEX-a material during the manufacturing of the pipes. Tert-butyl alcohol (TBA) concentrations were high during the first months after commissioning of use. The stagnation time of the drinking water in contact with the PEX-a material before the actual water sample was taken had a major impact on analyzed migration of organic compounds. Hence, the amount of organic compounds able to migrate from materials into the drinking water will increase when the stagnation time increases. In this study, the water samples were taken after overnight stagnation, whereas in normal use it is advisable to run water properly before drinking it. Instructions will be needed for the average user to avoid harmful health effects.

Aldehyde dehydrogenase 2 deficiency significantly exacerbates tert-butyl alcohol-induced toxicity in mice

Owing to the use of ethyl tert-butyl ether (ETBE) as a fuel additive, the possible adverse effects of ETBE exposure have become a public concern. Our previous study showed that ETBE-induced toxicity in aldehyde dehydrogenase 2 (Aldh2) gene knockout (KO) mice was caused by its primary metabolite acetaldehyde, which was toxic. However, it is unclear whether tert-butyl alcohol (TBA), another main metabolite of ETBE, plays a role in ETBE-induced toxicity. To investigate this relationship, we analyzed the changes of TBA concentrations in tissues after ETBE exposure, and then evaluated the toxicity after direct TBA treatment in both KO and wild-type (WT) mice. An exposure to 500 ppm ETBE via inhalation resulted in the formation of its three metabolites, TBA, 2-methyl-1,2-propanediol and ethanol, whose concentrations in the liver, brain, fat and testis of male KO mice were significantly higher than the corresponding concentrations observed in male WT mice. Direct treatment to TBA (20 mg/mL of drinking water) caused significant changes in relative organ weights and histopathology, and increased levels of genetic damages in both types of mice. These toxic effects were also seen in KO mice exposed to a lower concentration of TBA (5 mg/mL), which was associated with increased oxidative stress in serum (reduced glutathione and reduced glutathione/oxidized glutathione ratio decreased). Our findings indicate that ALDH2 is involved in the metabolism of ETBE and TBA, and ALDH2 deficiency could greatly increase the sensitivity to TBA-induced toxicity.

Lessons learned from a case of tert-butyl glucuronide excretion in urine - "New" psychoactive alcohols knocking on the back door?

BACKGROUND

Ethyl glucuronide (EtG) in urine is considered a marker of recent ethanol consumption or ethanol exposition. tert-Butanol is primarily used as a solvent and intermediate chemical. Like tert-amyl alcohol, tert-butanol is discussed in Internet forums as ethanol replacement. We discuss false-positive immunological EtG screenings by excretion of different alcohol glucuronides (EtG homologs), mainly tert-butyl glucuronide in urine of a polytoxikomanic in-patient.

METHODS

Three consecutive urine samples from an in-patient with a long history of multiple substance abuse including solvents were analyzed by DRI EtG enzyme immunoassay (ThermoFisher Scientific Microgenics) on a Beckman Coulter AU680 analyzer, an in-house LC-MS/MS for EtG, 1-propyl, 2-propyl, 1-butyl, 2-butyl, and tert-butyl glucuronide, and an in-house headspace GC-FID of free congener substances methanol, 1-propanol, 2-butanone, 2-butanol, isobutanol, 1-butanol, 3-methyl-1-butanol, 2-methyl-1-butanol, and additionally for ethanol, acetone, 2-propanol, tert-butanol and 2-methyl-2-butanol.

RESULTS

EtG immunoassay yielded two positive urine samples (0.2 and 0.6mg/L or 0.1 and 0.2mg/g creatinine; cut-off 0.1mg/L) which were tested EtG negative by LC-MS/MS (cut-off 0.1mg/L) but positive for tert-butyl glucuronide (3.7 and 27.1mg/L), 2-butyl glucuronide (1.1 and 3.5mg/L), and 2-propyl glucuronide (0.1 and 0.4mg/L). Headspace GC-FID detected tert-butanol (0.97 and 4.01mg/L), methanol (0.96 and 0.62mg/L), 2-butanone (0.84 and 1.65mg/L), and 2-butanol (0.04 and 0.09mg/L), but no ethanol and no 2-methyl-2-butanol.

CONCLUSION

Cross-reaction of EtG homologs, mainly tert-butyl glucuronide after suspected tert-butanol or isobutane abuse, explains the false-positive EtG immunoassay findings. Future investigations could address the usefulness of alcohol glucuronides (EtG homologs) in urine as (a) biomarkers of an exposition to alkans or their corresponding alcohol metabolites and (b) as markers for using "old"-well known alcohols like tert-butanol or tert-amyl alcohol as easy to obtain, cheap, potent and "undetectable" ethanol replacements or "New" Psychoactive Alcohols.

Synchrotron Photoionization Investigation of the Oxidation of Ethyl tert-Butyl Ether

The oxidation of ethyl tert-butyl ether (ETBE), a widely used fuel oxygenated additive, is investigated using Cl atoms as initiators in the presence of oxygen. The reaction is carried out at 293, 550, and 700 K. Reaction products are probed by a multiplexed chemical kinetics photoionization mass spectrometer coupled with the synchrotron radiation produced at the Advanced Light Source (ALS) of the Lawrence Berkeley National Laboratory. Products are identified on the basis of mass-to-charge ratio, ionization energies, and shape of photoionization spectra. Reaction pathways are proposed together with detected primary products.

Scientific opinion on the evaluation of substances as acceptable previous cargoes for edible fats and oils

Shipping of edible fats and oils into Europe is permitted in bulk tanks, provided that the previous cargo is included in a positive list. The European Commission requested EFSA to evaluate the acceptability as previous cargoes for fats and oils the substances calcium lignosulphonate, methyl acetate, ethyl tert-butyl ether (ETBE) and ammonium sulphate. The evaluation was based on the same criteria as those used for the evaluation of the substances currently on the list in the Annex to Commission Directive 96/3/EC as acceptable previous cargoes for edible fats and oils. Methyl acetate and ETBE meet the criteria for acceptability as previous cargoes. Due to uncertainties, mainly with regard to the composition and toxicity of the low molecular mass fraction, and the fact that the toxicological database is limited to the 40-65 grade and does not cover all grades of calcium lignosulphonate shipped as previous cargoes, the EFSA Panel on Contaminants in the Food Chain (CONTAM Panel) concluded that calcium lignosulphonate does not meet the criteria for acceptability as a previous cargo. Only food-grade ammonium sulphate meets the criteria for acceptability as a previous cargo due to uncertainties about impurities in other (non-food) grades.

Physiologically based pharmacokinetic model for ethyl tertiary-butyl ether and tertiary-butyl alcohol in rats: Contribution of binding to α2u-globulin in male rats and high-exposure nonlinear kinetics to toxicity and cancer outcomes

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 AUC_0-∞ 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 AUC_0-∞ 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.

Promotion of liver and kidney carcinogenesis by ethyl tertiary-butyl ether (ETBE) in male Wistar rats

Tumor-promoting effects of ethyl tertiary-butyl ether (ETBE) were investigated in a 2-stage carcinogenesis bioassay with regard to hepatic and renal carcinogenesis in rats. Male 6-week-old Wistar rats were given drinking water containing N-ethyl-N-(2-hydroxyethyl)nitrosamine (EHEN), as an initiator, at a dose of 500 ppm for 2 weeks. Starting one week thereafter, the animals were administered ETBE at dose levels of 0 (control), 100, 300, 500 or 1,000 mg/kg/day by gavage for 19 weeks from week 4 to 22. Necropsy of all rats was performed at week 23, and livers and kidneys were examined histopathologically. Incidences of hepatocellular adenomas, and those of combined hepatocellular adenomas and carcinomas were significantly elevated in rats given 1,000 mg/kg/day ETBE, but not 100‒500 mg/kg/day ETBE, and there was a significant increase in the average numbers of lesions. No significant differences in incidences and average numbers of renal tubule neoplasms were found in rats administered 100‒1,000 mg/kg/day ETBE. However, the average numbers of atypical tubule hyperplasias, considered to be preneoplastic lesions, were significantly increased in rats given ETBE at 1,000 mg/kg/day, but not in rats given 500 mg/kg/day or lower doses. Thus, these results imply that ETBE has hepatic and renal tumor-promoting activities that affect EHEN-induced carcinogenesis in male rats, and the no-observed-effect level is 500 mg/kg/day under the present experimental conditions.

Genome-Wide Association Study with Targeted and Non-targeted NMR Metabolomics Identifies 15 Novel Loci of Urinary Human Metabolic Individuality

Genome-wide association studies with metabolic traits (mGWAS) uncovered many genetic variants that influence human metabolism. These genetically influenced metabotypes (GIMs) contribute to our metabolic individuality, our capacity to respond to environmental challenges, and our susceptibility to specific diseases. While metabolic homeostasis in blood is a well investigated topic in large mGWAS with over 150 known loci, metabolic detoxification through urinary excretion has only been addressed by few small mGWAS with only 11 associated loci so far. Here we report the largest mGWAS to date, combining targeted and non-targeted ¹H NMR analysis of urine samples from 3,861 participants of the SHIP-0 cohort and 1,691 subjects of the KORA F4 cohort. We identified and replicated 22 loci with significant associations with urinary traits, 15 of which are new (HIBCH, CPS1, AGXT, XYLB, TKT, ETNPPL, SLC6A19, DMGDH, SLC36A2, GLDC, SLC6A13, ACSM3, SLC5A11, PNMT, SLC13A3). Two-thirds of the urinary loci also have a metabolite association in blood. For all but one of the 6 loci where significant associations target the same metabolite in blood and urine, the genetic effects have the same direction in both fluids. In contrast, for the SLC5A11 locus, we found increased levels of myo-inositol in urine whereas mGWAS in blood reported decreased levels for the same genetic variant. This might indicate less effective re-absorption of myo-inositol in the kidneys of carriers. In summary, our study more than doubles the number of known loci that influence urinary phenotypes. It thus allows novel insights into the relationship between blood homeostasis and its regulation through excretion. The newly discovered loci also include variants previously linked to chronic kidney disease (CPS1, SLC6A13), pulmonary hypertension (CPS1), and ischemic stroke (XYLB). By establishing connections from gene to disease via metabolic traits our results provide novel hypotheses about molecular mechanisms involved in the etiology of diseases.

Human metabolism is influenced by genetic and environmental factors defining a person’s metabolic individuality. This individuality is linked to personal differences in the ability to react on metabolic challenges and in the susceptibility to specific diseases. By investigating how common variants in genetic regions (loci) affect individual blood metabolite levels, the substantial contribution of genetic inheritance to metabolic individuality has been demonstrated previously. Meanwhile, more than 150 loci influencing metabolic homeostasis in blood are known. Here we shift the focus to genetic variants that modulate urinary metabolite excretion, for which only 11 loci were reported so far. In the largest genetic study on urinary metabolites to date, we identified 15 additional loci. Most of the 26 loci also affect blood metabolite levels. This shows that the metabolic individuality seen in blood is also reflected in urine, which is expected when urine is regarded as “diluted blood”. Nonetheless, we also found loci that appear to primarily influence metabolite excretion. For instance, we identified genetic variants near a gene of a transporter that change the capability for renal re-absorption of the transporter’s substrate. Thus, our findings could help to elucidate molecular mechanisms influencing kidney function and the body’s detoxification capabilities.

Induction of cell proliferation in the rat liver by the short-term administration of ethyl tertiary-butyl ether

In the present study, in continuation of our previous experiment in order to investigate the mode of action (MOA) of ethyl tertiary-butyl ether (ETBE) hepatotumorigenicity in rats, we aimed to examine alterations in cell proliferation, that are induced by short-term administration of ETBE. F344 rats were administered ETBE at doses of 0, and 1,000 mg/kg body weight twice a day by gavage for 3, 10, 17 and 28 days. It was found that the previously observed significant increase of P450 total content and hydroxyl radical levels after 7 days of ETBE administration, and 8-OHdG formation at day 14, accompanied by accumulation of CYP2B1/2B2, CYP3A1/3A2, CYP2C6, CYP2E1 and CYP1A1 and downregulation of DNA oxoguanine glycosylase 1, was preceded by induction of cell proliferation at day 3. Furthermore, we observed an increase in regenerative cell proliferation as a result of ETBE treatment at day 28, followed by induction of cell cycle arrest and apoptosis by day 14. These results indicated that short-term administration of ETBE led to a significant early increase in cell proliferation activity associated with induction of oxidative stress, and to a regenerative cell proliferation as an adaptive response, which could contribute to the hepatotumorigenicity of ETBE in rats.

Promotion of liver and kidney carcinogenesis by ethyl tertiary-butyl ether (ETBE) in male Wistar rats

Tumor-promoting effects of ethyl tertiary-butyl ether (ETBE) were investigated in a 2-stage carcinogenesis bioassay with regard to hepatic and renal carcinogenesis in rats. Male 6-week-old Wistar rats were given drinking water containing N-ethyl-N-(2-hydroxyethyl)nitrosamine (EHEN), as an initiator, at a dose of 500 ppm for 2 weeks. Starting one week thereafter, the animals were administered ETBE at dose levels of 0 (control), 100, 300, 500 or 1,000 mg/kg/day by gavage for 19 weeks from week 4 to 22. Necropsy of all rats was performed at week 23, and livers and kidneys were examined histopathologically. Incidences of hepatocellular adenomas, and those of combined hepatocellular adenomas and carcinomas were significantly elevated in rats given 1,000 mg/kg/day ETBE, but not 100‒500 mg/kg/day ETBE, and there was a significant increase in the average numbers of lesions. No significant differences in incidences and average numbers of renal tubule neoplasms were found in rats administered 100‒1,000 mg/kg/day ETBE. However, the average numbers of atypical tubule hyperplasias, considered to be preneoplastic lesions, were significantly increased in rats given ETBE at 1,000 mg/kg/day, but not in rats given 500 mg/kg/day or lower doses. Thus, these results imply that ETBE has hepatic and renal tumor-promoting activities that affect EHEN-induced carcinogenesis in male rats, and the no-observed-effect level is 500 mg/kg/day under the present experimental conditions.

Ethyl tert-butyl ether (ETBE)-degrading microbial communities in enrichments from polluted environments

The ethyl tert-butyl ether (ETBE) degradation capacity and phylogenetic composition of five aerobic enrichment cultures with ETBE as the sole carbon and energy source were studied. In all cases, ETBE was entirely degraded to biomass and CO2. Clone libraries of the 16S rRNA gene were prepared from each enrichment. The analyses of the DNA sequences obtained showed different taxonomic compositions with a majority of Proteobacteria in three cases. The two other enrichments have different microbiota with an abundance of Acidobacteria in one case, whereas the microbiota in the second was more diverse (majority of Actinobacteria, Chlorobi and Gemmatimonadetes). Actinobacteria were detected in all five enrichments. Several bacterial strains were isolated from the enrichments and five were capable of degrading ETBE and/or tert-butyl alcohol (TBA), a degradation intermediate. The five included three Rhodococcus sp. (IFP 2040, IFP 2041, IFP 2043), one Betaproteobacteria (IFP 2047) belonging to the Rubrivivax/Leptothrix/Ideonella branch, and one Pseudonocardia sp. (IFP 2050). Quantification of these five strains and two other strains, Rhodococcus sp. IFP 2042 and Bradyrhizobium sp. IFP2049, which had been previously isolated from one of the enrichments was carried out on the different enrichments based on quantitative PCR with specific 16S rRNA gene primers and the results were consistent with the hypothesized role of Actinobacteria and Betaproteobacteria in the degradation of ETBE and the possible role of Bradyrhizobium strains in the degradation of TBA.

Health assessment of gasoline and fuel oxygenate vapors: micronucleus and sister chromatid exchange evaluations

Micronucleus and sister chromatid exchange (SCE) tests were performed for vapor condensate of baseline gasoline (BGVC), or gasoline with oxygenates, methyl tert-butyl ether (G/MTBE), ethyl tert butyl ether (G/ETBE), t-amyl methyl ether (G/TAME), diisopropyl ether (G/DIPE), t-butyl alcohol (TBA), or ethanol (G/EtOH). Sprague Dawley rats (the same 5/sex/group for both endpoints) were exposed to 0, 2000, 10,000, or 20,000mg/m(3) of each condensate, 6h/day, 5days/week over 4weeks. Positive controls (5/sex/test) were given cyclophosphamide IP, 24h prior to sacrifice at 5mg/kg (SCE test) and 40mg/kg (micronucleus test). Blood was collected from the abdominal aorta for the SCE test and femurs removed for the micronucleus test. Blood cell cultures were treated with 5μg/ml bromodeoxyuridine (BrdU) for SCE evaluation. No significant increases in micronucleated immature erythrocytes were observed for any test material. Statistically significant increases in SCE were observed in rats given BGVC alone or in female rats given G/MTBE. G/TAME induced increased SCE in both sexes at the highest dose only. Although DNA perturbation was observed for several samples, DNA damage was not expressed as increased micronuclei in bone marrow cells. Inclusion of oxygenates in gasoline did not increase the effects of gasoline alone or produce a cytogenetic hazard.

No Promoting Effect of Ethyl Tertiary-butyl Ether (ETBE) on Rat Urinary Bladder Carcinogenesis Initiated with N-Butyl-N-(4-hydroxybutyl)nitrosamine

The effects of ethyl tertiary-butyl ether (ETBE) on two-stage urinary bladder carcinogenesis in male F344 rats initiated with N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) were investigated at various dose levels with regard to possible promoting activity. Groups of 30 rats were given drinking water containing 500 ppm BBN, as an initiator, for 4 weeks and starting one week thereafter received ETBE by gavage (daily, 7 days/week) at dose levels of 0 (control), 100, 300, 500 or 1000 mg/kg/day until experimental week 36. No statistically significant differences in incidences of preneoplastic lesions, papillomas, and carcinomas of the urinary bladder were evident in rats treated with 100–1000 mg/kg/day ETBE as compared with control values. Furthermore, the average numbers of preneoplastic or neoplastic lesions per unit length of basement membrane in rats given 100–1000 mg/kg/day ETBE were also comparable to control values. However, papillomatosis of the urinary bladder was found in 4 out of 30 rats (13%) in the group given 1000 mg/kg/day ETBE, and soft stones in the urinary bladder were found in 3 out of these 4 rats. The results thus demonstrated that ETBE did not exert promotional activity on urinary bladder carcinogenesis. However, papillomatosis of the urinary bladder developed in small numbers of the rats given ETBE at 1000 mg/kg/day but not in rats given 500 mg/kg/day or lower doses.

A subchronic (180-day) oral toxicity study of ethyl tertiary-butyl ether, a bioethanol, in rats

A subchronic (180-day) toxicity study was conducted to evaluate the effects of ethyl tertiary-butyl ether (ETBE), a biomass fuel, in male and female rats. ETBE was administered at dose levels of 0, 5, 25, 100 and 400 mg/kg/body weight (b.w.)/day by gavage. No treatment-related adverse effects were observed at 5, 25 or 100 mg/kg. Centrilobular hypertrophy of hepatocytes was observed in males and females and their relative liver weights were increased, suggesting enhanced metabolic activity. From these results, we concluded that the no observed adverse effect level of ETBE was 100 mg/kg b.w./day under the conditions tested.

Lack of micronucleus induction activity of ethyl tertiary-butyl ether in the bone marrow of F344 rats by sub-chronic drinking-water treatment, inhalation exposure, or acute intraperitoneal injection

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.

Oxidative stress in the carcinogenicity of chemical carcinogens

This review highlights several in vivo studies utilizing non-genotoxic and genotoxic chemical carcinogens, and the mechanisms of their high and low dose carcinogenicities with respect to formation of oxidative stress. Here, we survey the examples and discuss possible mechanisms of hormetic effects with cytochrome P450 inducers, such as phenobarbital, a-benzene hexachloride and 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane. Epigenetic processes differentially can be affected by agents that impinge on oxidative DNA damage, repair, apoptosis, cell proliferation, intracellular communication and cell signaling. Non-genotoxic carcinogens may target nuclear receptors and induce post-translational modifications at the protein level, thereby impacting on the stability or activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. We further discuss role of oxidative stress focusing on the low dose carcinogenicities of several genotoxic carcinogens such as a hepatocarcinogen contained in seared fish and meat, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, arsenic and its metabolites, and the kidney carcinogen potassium bromate.

Oxidative degradation of alternative gasoline oxygenates in aqueous solution by ultrasonic irradiation: mechanistic study

Widespread pollution has been associated with gasoline oxygenates of branched ethers methyl tert-butyl ether (MTBE), di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl ether (TAME) which enter groundwater. The contaminated plume develops rapidly and treatment for the removal/destruction of these ethers is difficult when using conventional methods. Degradation of MTBE, with biological methods and advanced oxidation processes, are rather well known; however, fewer studies have been reported for degradation of alternative oxygenates. Degradation of alternative gasoline oxygenates (DIPE, ETBE, and TAME) by ultrasonic irradiation in aqueous oxygen saturation was investigated to elucidate degradation pathways. Detailed degradation mechanisms are proposed for each gasoline oxygenate. The common major degradation pathways are proposed to involve abstraction of α-hydrogen atoms by hydroxyl radicals generated during ultrasound cavitation and low temperature pyrolytic degradation of ETBE and TAME. Even some of the products from β-H abstraction overlap with those from high temperature pyrolysis, the effect of β-H abstraction was not shown clearly from product study because of possible 1,5 H-transfer inside cavitating bubbles. Formation of hydrogen peroxide and organic peroxides was also determined during sonolysis. These data provide a better understanding of the degradation pathways of gasoline oxygenates by sonolysis in aqueous solutions. The approach may also serve as a model for others interested in the details of sonolysis.

Effects of subchronic inhalation exposure to ethyl tertiary butyl ether on splenocytes in mice

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.

Differential genotoxic effects of subchronic exposure to ethyl tertiary butyl ether in the livers of Aldh2 knockout and wild-type mice

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.

Oral subchronic immunotoxicity study of ethyl tertiary butyl ether in the rat

The potential for immunotoxicological effects of ethyl tertiary butyl ether (ETBE, CAS RN 637-92-3) was studied in young adult female Crl:CD(SD) rats following subchronic oral exposures. Rats were exposed by gavage once daily for 28 consecutive days to 0, 250, 500, or 1000 mg ETBE/kg body weight (BW)/day; a concurrent positive control group received four intraperitoneal injections of at 50 mg cyclophosphamide monohydrate (CPS)/kg/day on study Days 24-27. Immunotoxicity was evaluated using a splenic antibody-forming cell (AFC) assay to assess T-cell-dependent antibody responses in rats sensitized with sheep red blood cells (SRBC). All rats survived to the scheduled necropsy. There were no effects on clinical observations, body weights, feed or water consumption, or macroscopic pathology findings in the ETBE-treated rats. No ETBE-related effects were observed on absolute or relative (to final body weight) spleen or thymus weights, spleen cellularity, or on the specific (AFC/10(6) spleen cells) or total activity (AFC/spleen) of splenic IgM AFC to the T-cell-dependent antigen SRBC. CPS produced expected effects consistent with its known immunosuppressive properties and validated the appropriateness of the AFC assay. Based on the results of this study, ETBE did not suppress the humoral component of the immune system in female rats. The no-observed-effect level for immunotoxicity was the highest dosage tested at 1000 mg/kg/day.

Aldh2 knockout mice were more sensitive to DNA damage in leukocytes due to ethyl tertiary butyl ether exposure

To clarify the genotoxicity of ethyl tertiary butyl ether (ETBE), a gasoline additive, male and female C57BL/6 mice of Aldh2+/+ and Aldh2-/- genotypes, aged 8 wk, were exposed to 0, 500, 1,750, or 5,000 ppm ETBE for 6 h/day, 5 d per week for 13 wk. DNA damage in leukocytes was measured by the alkaline comet assay and expressed quantitatively as Tail Intensity (TI). For male mice, TI was significantly higher in all three groups exposed to ETBE than in those without exposure within Aldh2-/- mice, whereas within Aldh2+/+ mice, TI increased only in those exposed to 5,000 ppm of ETBE as compared with mice without exposure. For female mice, a significant increase in TI values was observed in the group exposed to 5,000 ppm of ETBE as compared with those without exposure within Aldh2-/- mice; TI in Aldh2-/- mice exposed to 1,750 and 5,000 ppm was significantly higher than in Aldh2+/+ mice without exposure. TI did not significantly increase in any of the groups exposed to ETBE within female Aldh2+/+ mice. Based on the results we suggest that Aldh2-/- mice are more sensitive to DNA damage caused by ETBE than Aldh2+/+ mice and that males seem more susceptible to this effect than females.

Ethyl t-butyl ether: review of reproductive and developmental toxicity

Ethyl t-butyl ether (ETBE) is a motor fuel oxygenate used in reformulated gasoline. Knowledge of developmental and reproductive toxicity potential of ETBE is critical for making informed decisions about acceptance and regulations. This review discusses toxicology studies providing information about effects on reproduction and the conceptus. Seven GLP-compliant studies following widely accepted protocols have focused specifically on developmental and reproductive toxicity (DART) in rats and rabbits exposed to ETBE by gavage with doses up to 1,000 mg/kg body weight/day, the limit specified in standardized test guidelines. Other repeat-dose general toxicology studies have administered ETBE to rodents for up to 180 days, and included reproductive organ weights, histology, or other indications of reproductive system structure or function. DART potential of the main ETBE metabolite t-butyl alcohol and class-related MTBE has also been studied. More GLP-compliant studies exist for evaluating ETBE using well-established, currently recommended protocols than are available for many other chemicals used today. The database for determining ETBE DART potential is adequate, although not all study details are currently easily accessible for peer-review. ETBE does not appear to be selectively toxic to reproduction or embryofetal development in the absence of other manifestations of general toxicity. Studies using recommended methods for sample preservation and analysis have shown no targeted effect on the reproductive system. No embryofetal effects were observed in rabbits. Early postnatal rat pup deaths show no clear dose-response and have largely been attributed to total litter losses with accompanying evidence of maternal neglect or frank maternal morbidity.

Inhibition of IgE-induced mast cell activation by ethyl tertiary-butyl ether, a bioethanol-derived fuel oxygenate

Objectives

The effect of ethyl tertiary-butyl ether (ETBE), which is widely used as a fuel oxygenate commonly produced from bioethanol, on immunoglobulin (Ig)E-dependent mast cell activation was investigated.

Methods

The rat mast cell line RBL2H3 sensitised with monoclonal anti-ovalbumin IgE was challenged with ovalbumin in the presence or absence of ETBE, tert-butanol (TBA), which is the main metabolite of ETBE in humans, and ethanol. Degranulation of RBL2H3 was examined by the release of β-hexosaminidase. To understand the mechanisms responsible for regulating mast cell function, the effects of ETBE, TBA and ethanol on the levels of intracellular calcium, phosphorylation of Akt (as a marker of phosphatidylinositol 3-kinase) and global tyrosine phosphorylation were also measured as indicators of mast cell activation.

Key findings

In the presence of ETBE, TBA or ethanol, IgE-induced release of β-hexosaminidase was decreased. These compounds also attenuated the IgE-mediated increase in the levels of intracellular Ca2+, phosphorylation of Akt and global tyrosine phosphorylation in RBL2H3 cells.

Conclusions

ETBE, TBA and ethanol inhibited mast cell degranulation by inhibiting the increase in intracellular calcium ion concentration and activation of phosphatidylinositol 3-kinase and protein tyrosine kinase activation, suggesting that exposure to ETBE might affect immune responses, particularly in allergic diseases.

Effect of ETBE on reproductive steroids in male rats and rat Leydig cell cultures

These experiments were conducted to follow up on a report of testis seminiferous tubular degeneration in Fischer 344 rats treated with high doses of ethyl t-butyl ether (ETBE). Also, high doses of a related compound, methyl t-butyl ether (MTBE), had been shown to reduce circulating testosterone (T) in rats. Isolated rat Leydig cells were used to compare hCG-stimulated T production following exposure to ETBE, MTBE, and their common main metabolite, TBA. In addition, male Fischer 344 rats were gavaged daily with 600 mg/kg, 1200 mg/kg or 1800 mg/kg ETBE in corn oil (n=12) for 14 days, the 1200 mg/kg dose chosen for comparison with a prior 14-day MTBE gavage experiment. In cell culture experiments, TBA was more potent than either ETBE or MTBE, both of which caused similar inhibition of T production at equimolar concentrations. In the in vivo study, no significant plasma T reduction was seen 1h after the final 1200 mg/kg ETBE dose, whereas 1200 mg/kg MTBE had significantly lowered T when administered similarly to Sprague-Dawley rats. Some rats treated with 1800 mg/kg ETBE had noticeably lower T levels, and the group average T level was 66% of corn oil vehicle control (p>0.05) with high variability also evident in ETBE-treated rats. 17beta-Estradiol had been increased by 1200 mg/kg MTBE, and was elevated in the 1200 and 1800 mg/kg ETBE dose groups (p<0.05), both groups also experiencing significantly reduced body weight gain. None of these effects were seen with 600 mg/kg/day ETBE. No definitive evidence of androgen insufficiency was seen in accessory organ weights, and no testicular pathology was observed after 14 days in a small subset of 1800 mg/kg ETBE-treated animals. Like MTBE, ETBE appears to be capable of altering reproductive steroid levels in peripheral blood sampled 1h after treatment, but only with extremely high doses that inhibit body weight gain and may produce mortality.