The effects of prenatal tertiary butanol administration in CBA/J and C57BL/6J mice

Assessment of the genotoxicity of tert-butyl alcohol in an in vivo thyroid comet assay

Chronic exposure to high (20,000 ppm) concentrations of tert-butyl alcohol (TBA) in drinking water, equivalent to ~2100 mg/kg bodyweight per day, is associated with slight increases in the incidence of thyroid follicular cell adenomas and carcinomas in mice, with no other indications of carcinogenicity. In a recent toxicological review of TBA, the U.S. EPA determined that the genotoxic potential of TBA was inconclusive, largely based on non-standard studies such as in vitro comet assays. As such, the potential role of genotoxicity in the mode of action of thyroid tumors and therefore human relevance was considered uncertain. To address the potential role of genotoxicity in TBA-associated thyroid tumor formation, CD-1 mice were exposed up to a maximum tolerated dose of 1500 mg/kg-day via oral gavage for two consecutive days and DNA damage was assessed with the comet assay in the thyroid. Blood TBA levels were analyzed by headspace GC-MS to confirm systemic tissue exposure. At study termination, no significant increases (DNA breakage) or decreases (DNA crosslinks) in %DNA tail were observed in TBA exposed mice. In contrast, oral gavage of the positive control ethyl methanesulfonate significantly increased %DNA tail in the thyroid. These findings are consistent with most genotoxicity studies on TBA and provide mechanistic support for non-linear, threshold toxicity criteria for TBA. While the mode of action for the thyroid tumors remains unclear, linear low dose extrapolation methods for TBA appear more a matter of policy than science.

Assessment of the reproductive toxicity of inhalation exposure to ethyl tertiary butyl ether in male mice with normal, low active and inactive ALDH2

No data are available regarding aldehyde dehydrogenase 2 (ALDH2) polymorphisms related to the reproductive toxicity possibly caused by ethyl tertiary butyl ether (ETBE). In this study, two inhalation experiments were performed in Aldh2 knockout (KO), heterogeneous (HT) and wild type (WT) C57BL/6 male mice exposed to ETBE, and the data about general toxicity, testicular histopathology, sperm head numbers, sperm motility and sperm DNA damage were collected. The results showed that the 13-week exposure to 0, 500, 1,750 and 5,000 ppm ETBE significantly decreased sperm motility and increased levels of sperm DNA strand breaks and 8-hydroxy-deoxyguanosine in both WT and KO mice, the effects were found in 1,750 and 5,000 ppm groups of WT mice, and all of the three exposed groups of KO mice compared to the corresponding control; furthermore, ETBE also caused decrease in the relative weights of testes and epididymides, the slight atrophy of seminiferous tubules of testis and reduction in sperm numbers of KO mice exposed to ≥500 ppm. In the experiment of exposure to lower concentrations of ETBE (0, 50, 200 and 500 ppm) for 9 weeks, the remarkable effects of ETBE on sperm head numbers, sperm motility and sperm DNA damage were further observed in KO and HT mice exposed to 200 ppm ETBE, but not in WT mice. Our findings suggested that only exposure to high concentrations of ETBE might result in reproductive toxicity in mice with normal active ALDH2, while low active and inactive ALDH2 enzyme significantly enhanced the ETBE-induced reproductive toxicity in mice, even exposed to low concentrations of ETBE, mainly due to the accumulation of acetaldehyde as a primary metabolite of ETBE.

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.

Amended final report of the safety assessment of t-Butyl Alcohol as used in cosmetics

t-Butyl Alcohol (t-BuOH) is a tertiary aliphatic alcohol that is used as a solvent or an alcohol denaturant and as a perfume carrier in cosmetics. t-BuOH was reported as an ingredient in 32 formulations of eye makeup, fragrance, and shaving preparations, at concentrations ranging from 0.00001% and 0.3%. There is little acute oral toxicity in animals; e.g., the acute oral LD(50) in rats was 3.0 to 3.7 g/kg. In short-term oral studies in rats, t-BuOH at 2% (w/v) or less in drinking water did not cause gross organ or tissue damage in mice, although weight loss was reported and microscopic damage to livers and kidney and alterations such as centrilobular necrosis, vacuolation in hepatocytes, and loss of hepatic architecture were noted. Subchronic oral dosing with t-BuOH increased the mineralization of the kidney, nephropathy, and urinary bladder transitional cell epithelial hyperplasia in rats; and liver damage, chronic inflammation, hyperplasia of transitional cell epithelium urinary, and proliferative changes including hyperplasia and neoplasia in the thyroid in mice. Male rats exposed to t-BuOH were susceptible to alpha 2mu-globulin nephropathy. t-BuOH (99.9%) was a moderate to severe ocular irritant to rabbits and caused mild to moderate dermal irritation to rabbits. It was not considered to be a primary dermal irritant to rabbits. In animal studies, fetotoxicity generally increased with concentration, and fetal weights were slightly depressed at concentrations of 0.5% to 1% t-BuOH. t-BuOH produced a significant increase in the number of resorptions per litter. There was also a significant decrease in the number of live fetuses per litter. t-BuOH reduced maternal weight gain, litter sizes, birth weights, and weights at weaning, and increased perinatal and postnatal mortality. t-BuOH was not mutagenic in several bacterial and mammalian test systems. The principal effects from 2 years of exposure to t-BuOH in drinking water (up to 10 mg/ml for rats and 20 mg/ml for mice) were proliferative lesions (hyperplasia, adenoma, and carcinoma) in the kidneys of exposed male rats, and nephropathy in all exposed groups of female rats. There was some evidence of carcinogenic activity, but it was not consistent between species, sexes, or doses. A repeat-insult patch test (RIPT) test showed no potential for eliciting either dermal irritation or sensitization by 100% t-BuOH. Dermatitis can result from dermal exposure of humans to t-BuOH. In consideration of these data, it was concluded that t-BuOH was (at most) a weak carcinogen and unlikely to have significant carcinogenic potential as currently used in cosmetic formulations. In addition, the renal tubule effects found in male rats were likely an effect of alpha 2mu-globulin. In consideration of the reproductive and developmental toxicity data, the increased incidence of still births occurred at high exposure levels and was likely secondary to maternal toxicity. Based on the available animal and clinical data in this report, it was concluded that t-BuOH is safe as used in cosmetic products.

Use of pure t-butanol as a solvent for freeze-drying: a case study

1-(2-Chloroethyl)-3-sarcosinamide-1-nitrosourea, (SarCNU) (NSC-364432) is a new antitumor drug that is of interest to the National Cancer Institute. It is intended for use as an intravenous injection. Although SarCNU is sufficiently soluble in water to obtain the desired dosage, it is highly unstable. Its T(90) in aqueous solution at room temperature is less than 6 h. Neat tertiary butyl alcohol (TBA), a low toxicity, high vapor pressure and low melting solvent, was determined to be an excellent freeze-drying medium. Lyophilization of SarCNU from pure TBA produces a uniform cake composed of needle-shaped crystals. Thermal analysis and gas chromatography indicate that the cake contains less than 0.001% residual solvent. The SarCNU cake can be readily reconstituted with either water or an aqueous solution of 40% propylene glycol and 10% ethanol. The reconstituted solutions are stable for 4 and 13 h, respectively.

Exposure of embryonic cells to alcohol: contrasting effects during preimplantation and postimplantation development

Alcohol is a known teratogen that causes a broad variety of developmental anomalies, including fetal growth retardation, craniofacial anomalies, and neurological disorders. The etiology of this multiple defect syndrome, known as fetal alcohol syndrome, has been studied in animal models that reproduce many of the attributes of the human disease. These studies show that ethanol is most teratogenic during organogenesis and development of the nervous system. The molecular basis of fetal alcohol effects has been further investigated using embryo and cell culture systems. Recent studies show that signal transduction pathways controlling cell proliferation are perturbed during ethanol exposure. Ethanol can induce the release of intracellular calcium stores, which stimulates the cell cycle, and it also up-regulates the expression of myc proteins associated with cell proliferation. Increased proliferation is advantageous during the preimplantation period, but ethanol interference with terminal differentiation events within developing tissues during organogenesis may underlie alcohol teratogenicity.