The in vivo metabolism of tertiary butanol by adult rats

Ethanol itself is a holoprosencephaly-inducing teratogen

Ethanol is a teratogen, inducing a variety of structural defects in developing humans and animals that are exposed in utero. Mechanisms of ethanol teratogenicity in specific defects are not well understood. Oxidative metabolism of ethanol by alcohol dehydrogenase or cytochrome P450 2E1 has been implicated in some of ethanol's teratogenic effects, either via production of acetaldehyde or competitive inhibition of retinoic acid synthesis. Generalized oxidative stress in response to ethanol may also play a role in its teratogenicity. Among the developmental defects that ethanol has been implicated in is holoprosencephaly, a failure to define the midline of the forebrain and midface that is associated with a deficiency in Sonic hedgehog pathway function. Etiologically, holoprosencephaly is thought to arise from a complex combination of genetic and environmental factors. We have developed a gene-environment interaction model of holoprosencephaly in mice, in which mutation of the Sonic hedgehog coreceptor, Cdon, synergizes with transient in utero exposure to ethanol. This system was used to address whether oxidative metabolism is required for ethanol's teratogenic activity in holoprosencephaly. We report here that t-butyl alcohol, which is neither a substrate nor an inhibitor of alcohol dehydrogenases or Cyp2E1, is a potent inducer of holoprosencephaly in Cdon mutant mice. Additionally, antioxidant treatment did not prevent ethanol- or t-butyl alcohol-induced HPE in these mice. These findings are consistent with the conclusion that ethanol itself, rather than a consequence of its metabolism, is a holoprosencephaly-inducing teratogen.

3 Final Report on the Safety Assessment of t-Butyl Alcohol

The safety of this ingredient has not been documented and substantiated. The Cosmetic Ingredient Review Expert Panel cannot conclude that t-Butyl Alcohol is safe for use in cosmetic products until such time that the appropriate safety data have been obtained and evaluated. The data that were available are documented in the report as well as the types of data that are required before a safety evaluation may be undertaken.

Reassessment of MTBE cancer potency considering modes of action for MTBE and its metabolites

A 1999 California state agency cancer potency (CP) evaluation of methyl tert-butyl ether (MTBE) assumed linear risk extrapolations from tumor data were plausible because of limited evidence that MTBE or its metabolites could damage DNA, and based such extrapolations on data from rat gavage and rat and mouse inhalation studies indicating elevated tumor rates in male rat kidney, male rat Leydig interstitial cells, and female rat leukemia/lymphomas. More recent data bearing on MTBE cancer potency include a rodent cancer bioassay of MTBE in drinking water; several new studies of MTBE genotoxicity; several similar evaluations of MTBE metabolites, formaldehyde, and tert-butyl alcohol or TBA; and updated evaluations of carcinogenic mode(s) of action (MOAs) of MTBE and MTBE metabolite's. The lymphoma/leukemia data used in the California assessment were recently declared unreliable by the U.S. Environmental Protection Agency (EPA). Updated characterizations of MTBE CP, and its uncertainty, are currently needed to address a variety of decision goals concerning historical and current MTBE contamination. To this end, an extensive review of data sets bearing on MTBE and metabolite genotoxicity, cytotoxicity, and tumorigenicity was applied to reassess MTBE CP and related uncertainty in view of MOA considerations. Adopting the traditional approach that cytotoxicity-driven cancer MOAs are inoperative at very low, non-cytotoxic dose levels, it was determined that MTBE most likely does not increase cancer risk unless chronic exposures induce target-tissue toxicity, including in sensitive individuals. However, the corresponding expected (or plausible upper bound) CP for MTBE conditional on a hypothetical linear (e.g., genotoxic) MOA was estimated to be ∼2 × 10(-5) (or 0.003) per mg MTBE per kg body weight per day for adults exposed chronically over a lifetime. Based on this conservative estimate of CP, if MTBE is carcinogenic to humans, it is among the weakest 10% of chemical carcinogens evaluated by EPA.

Tertiary-Butanol: a toxicological review

Tert-Butanol is an important intermediate in industrial chemical synthesis, particularly of fuel oxygenates. Human exposure to tert-butanol may occur following fuel oxygenate metabolism or biodegradation. It is poorly absorbed through skin, but is rapidly absorbed upon inhalation or ingestion and distributed to tissues throughout the body. Elimination from blood is slower and the half-life increases with dose. It is largely metabolised by oxidation via 2-methyl-1,2-propanediol to 2-hydroxyisobutyrate, the dominant urinary metabolites. Conjugations also occur and acetone may be found in urine at high doses. The single-dose systemic toxicity of tert-butanol is low, but it is irritant to skin and eyes; high oral doses produce ataxia and hypoactivity and repeated exposure can induce dependence. Tert-Butanol is not definable as a genotoxin and has no effects specific for reproduction or development; developmental delay occurred only with marked maternal toxicity. Target organs for toxicity clearly identified are kidney in male rats and urinary bladder, particularly in males, of both rats and mice. Increased tumour incidences observed were renal tubule cell adenomas in male rats and thyroid follicular cell adenomas in female mice and, non-significantly, at an intermediate dose in male mice. The renal adenomas were associated with alpha(2u)-globulin nephropathy and, to a lesser extent, exacerbation of chronic progressive nephropathy. Neither of these modes of action can function in humans. The thyroid tumour response could be strain-specific. No thyroid toxicity was observed and a study of hepatic gene expression and enzyme induction and thyroid hormone status has suggested a possible mode of action.

Acute alcohol intoxication increases REDD1 in skeletal muscle

BACKGROUND

The mechanism by which acute alcohol (EtOH) intoxication decreases basal muscle protein synthesis via inhibition of the Ser/Thr kinase mammalian target of rapamycin (mTOR) is poorly defined. In this regard, mTOR activity is impaired after over expression of the regulatory protein REDD1. Hence, the present study assessed the ability of REDD1 as a potential mediator of the EtOH-induced decrease in muscle protein synthesis.

METHODS

The effect of acute EtOH intoxication on REDD1 mRNA and protein was determined in striated muscle of rats and mouse myocytes using an RNase protection assay and Western blotting, respectively. Other components of the mTOR signaling pathway were also assessed by immunoblotting. For comparison, REDD1 mRNA/protein was also determined in the muscle of rats chronically fed an alcohol-containing diet for 14 weeks.

RESULTS

Intraperitoneal (IP) injection of EtOH increased gastrocnemius REDD1 mRNA in a dose- and time-dependent manner, and these changes were associated with reciprocal decreases in the phosphorylation of 4E-BP1, which is a surrogate marker for mTOR activity and protein synthesis. No change in REDD1 mRNA was detected in the slow-twitch soleus muscle or heart. Acute EtOH produced comparable increases in muscle REDD1 protein. The EtOH-induced increase in gastrocnemius REDD1 was independent of the route of EtOH administration (oral vs. IP), the nutritional state (fed vs. fasted), gender, and age of the rat. The nonmetabolizable alcohol tert-butanol increased REDD1 and the EtOH-induced increase in REDD1 was not prevented by pretreatment with the alcohol dehydrogenase inhibitor 4-methylpyrazole. In contrast, REDD1 mRNA and protein were not increased in the isolated hindlimb perfused with EtOH or in C2C12 myocytes incubated with EtOH, under conditions previously reported to decrease protein synthesis. Pretreatment with the glucocorticoid receptor antagonist RU486 failed to prevent the EtOH-induced increase in REDD1. Finally, the EtOH-induced increase in REDD1 was not associated with altered formation of the TSC1*TSC2 complex or the phosphorylation of TSC2 which is down stream in the REDD1 stress response pathway. In contradistinction to the changes observed with acute EtOH intoxication, REDD1 mRNA/protein was not changed in gastrocnemius from chronic alcohol-fed rats despite the reduction in 4E-BP1 phosphorylation.

CONCLUSIONS

These data indicate that in fast-twitch skeletal muscle (i) REDD1 mRNA/protein is increased in vivo by acute EtOH intoxication but not in response to chronic alcohol feeding, (ii) elevated REDD1 in response to acute EtOH appears due to the production of an unknown secondary mediator which is not corticosterone, and (iii) the EtOH-induced decrease in protein synthesis can be dissociated from a change in REDD1 suggesting that the induction of this protein is not responsible for the rapid decrease in protein synthesis after acute EtOH administration or for the development of alcoholic myopathy in rats fed an alcohol-containing diet.

Lead-induced catalase activity differentially modulates behaviors induced by short-chain alcohols

Acute lead administration produces a transient increase in brain catalase activity. This effect of lead has been used to assess the involvement of brain ethanol metabolism, and therefore centrally formed acetaldehyde, in the behavioral actions of ethanol. In mice, catalase is involved in ethanol and methanol metabolism, but not in the metabolism of other alcohols such as 1-propanol or tert-butanol. In the present study, we assessed the specificity of the effects of lead acetate on catalase-mediated metabolism of alcohols, and the ability of lead to modulate the locomotion and loss of the righting reflex (LRR) induced by 4 different short-chain alcohols. Animals were pretreated i.p. with lead acetate (100 mg/kg) or saline, and 7 days later were injected i.p. with ethanol (2.5 or 4.5 g/kg), methanol (2.5 or 6.0 g/kg), 1-propanol (0.5 or 2.5 g/kg) or tert-butanol (0.5 or 2.0 g/kg) for locomotion and LRR, respectively. Locomotion induced by ethanol was significantly potentiated in lead-treated mice, while methanol-induced locomotion was reduced by lead treatment. The loss of righting reflex induced by ethanol was shorter in lead-treated mice, and lead produced the opposite effect in methanol-treated mice. There was no effect of lead on 1-propanol or tert-butanol-induced behaviors. Lead treatment was effective in inducing catalase activity and protein both in liver and brain. These results support the hypothesis that the effects of lead treatment on ethanol-induced behaviors are related to changes in catalase activity, rather than some nonspecific effect that generalizes to all alcohols.

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.

Alcohol Intoxication Impairs Phosphorylation of S6K1 and S6 in Skeletal Muscle Independently of Ethanol Metabolism

BACKGROUND

The purpose of this study was to characterize the ability of alcohol to suppress insulin-like growth factor (IGF)-I stimulation of ribosomal S6 kinase 1 (S6K1) and 4E-BP1 phosphorylation, which are central elements in the signal transduction pathway used to coordinate the protein synthetic response and may contribute to the development of alcoholic myopathy.

METHODS

In vivo studies examined the dose and time dependency of the ability of alcohol to impair signal transduction under basal and IGF-I-stimulated conditions. Additional studies examined the effect of gender, nutritional state, and route of alcohol administration. A separate study determined the direct effects of alcohol on muscle metabolism by using the isolated perfused hindlimb preparation.

RESULTS

The phosphorylation of S6K1 and S6 in muscle was increased after injection of IGF-I in control rats. In contrast, IGF-I failed to stimulate S6K1 or S6 phosphorylation 2.5 hr after intraperitoneal administration of alcohol when the blood alcohol concentration was increased between approximately 165 and 300 mg/dl. With a maximal suppressive dose of alcohol, the inhibitory effect on S6K1/S6 phosphorylation was observed as early as 1 hr and for up to 8 hr. The ability of alcohol to impair phosphorylation of S6K1 and S6 was independent of gender (male versus female), nutritional status (fed versus fasted), and route of alcohol administration (intraperitoneal versus oral). Furthermore, the suppressive effect of alcohol was still observed in rats pretreated with 4-methylpyrazole, suggesting that the response was independent of the oxidative metabolism of ethanol. The direct effect of alcohol on IGF-stimulated S6K1/S6 phosphorylation was also present when the isolated hindlimb was perfused in situ with buffer containing alcohol. In contrast to S6K1, acute alcohol intoxication did not consistently impair the ability of IGF-I to stimulate 4E-BP1 phosphorylation under any of the experimental conditions.

CONCLUSIONS

These data indicate that acute alcohol intoxication selectively impairs IGF-I signaling via S6K1, but not 4E-BP1, and that this defect is independent of gender, nutritional state, route of administration, and alcohol metabolism. The IGF-I resistance may represent a participating mechanism by which alcohol directly limits the translation of selected messenger RNAs and, ultimately, protein synthesis in skeletal muscle.

Acute ethanol-mediated insulin resistance in the rat: the role of ethanol oxidation

Ethanol causes an acute and profound insulin resistance in humans and in the rat. Recent studies indicate that defects in skeletal muscle glucose uptake and utilization make a major contribution to this insulin resistance. In this study, we used the euglycaemic hyperinsulinaemic clamp to examine the role that hepatic ethanol oxidation via alcohol dehydrogenase (ADH) plays in the acute insulin resistance caused by ethanol in the rat. Treatment with the ADH inhibitor 4-methylpyrazole (4-MP) failed to abolish the insulin resistance as expressed as a decrease in the rate of glucose infusion required to maintain euglycaemia (GIR). A decrease in GIR was also observed in response to tert-butanol, an alcohol that is not a substrate for hepatic ADH. These results indicate that oxidation via ADH is not a prerequisite for the inhibition by ethanol of whole-body glucose utilization. In a separate study, we examined the relationship between blood ethanol concentration and GIR in order to determine the potency of ethanol in causing insulin resistance. These experiments showed that even at low blood concentrations (<2 mM), ethanol caused a profound decrease in GIR, similar in magnitude to that observed at higher blood concentrations (approximately 40 mM)

A histopathological study of liver and kidney in male Wistar rats treated with subtoxic doses of t-butyl alcohol and trichloroacetic acid

Tertiary butyl alcohol and trichloroacetic acid are known to be contaminants in drinking water. In order to evaluate the interactive toxicity of t-butyl alcohol with trichloroacetic acid, young male Wistar rats were dosed through water at a dose level of t-butyl alcohol (TBA)-0.5% (v/v), trichloroacetic acid (TCA)-25 ppm and a combined dose of TBA + TCA (0.5% v/v TBA-25 ppm TCA) for a period of 10 weeks ad libitum and were maintained on normal diet. The control animals received plain water and normal diet. The liver and kidney histology was undertaken to see whether subtoxic administration of TBA and TCA individually as well as combined administration for a period of 10 weeks would bring about any histological alterations. It was observed that TBA, TCA and TBA + TCA caused histological alterations in the liver such as centrilobular necrosis, vacuolation in hepatocytes and loss of hepatic architecture. TBA and TBA + TCA caused periportal proliferation and lymphocytic infiltration. Hypertrophy of hepatocytes in the periportal area was a characteristic feature in the liver of TCA treated rats. Moreover, in the histology of the kidney, in the three treated groups, degeneration of renal tubules, with syncitial arrangements of the nucleus of renal tubular epithelial cells was evident. In addition to this, degeneration of the basement membrane of the Bowmans capsule, diffused glomeruli and vacuolation of glomeruli was also evident in the three treated rat kidneys. Renal tubular proliferation in certain areas was also evident in certain areas of the kidney in TCA treated rats. The results indicate that, TBA and TCA do bring about alterations in histology of liver and kidney, but on combined administration, do not show enhanced toxicity in the form of increased hepatic and renal injury.

A physiologically-based pharmacokinetic model assessment of methyl t-butyl ether in groundwater for a bathing and showering determination

Methyl t-butyl ether (MTBE) is a gasoline additive that has appeared in private wells as a result of leaking underground storage tanks. Neurological symptoms (headache, dizziness) have been reported from household use of MTBE-affected water, consistent with animal studies showing acute CNS depression from MTBE exposure. The current research evaluates acute CNS effects during bathing/showering by application of physiologically-based pharmacokinetic (PBPK) techniques to compare internal doses in animal toxicity studies to human exposure scenarios. An additional reference point was the delivered dose associated with the acute Minimum Risk Level (MRL) for MTBE established by the Agency for Toxic Substances and Disease Registry. A PBPK model for MTBE and its principal metabolite, t-butyl alcohol (TBA) was developed and validated against published data in rats and humans. PBPK analysis of animal studies showed that acute CNS toxicity after MTBE exposure can be attributed principally to the parent compound since the metabolite (TBA) internal dose was below that needed for CNS effects. The PBPK model was combined with an exposure model for bathing and showering which integrates inhalation and dermal exposures. This modeling indicated that bathing or showering in water containing MTBE at 1 mg/L would produce brain concentrations approximately 1000-fold below the animal effects level and twofold below brain concentrations associated with the acute MRL. These findings indicate that MTBE water concentrations of 1 mg/L or below are unlikely to trigger acute CNS effects during bathing and showering. However, MTBE's strong odor may be a secondary but deciding factor regarding the suitability of such water for domestic uses.

Pharmacokinetics of tertiary butyl alcohol in male and female Fischer 344 rats

Tertiary butyl alcohol (TBA) is a small aliphatic alcohol with multiple industrial and scientific uses. A comprehensive pharmacokinetic profile for TBA has not been determined in rats. The purpose of this study was to fully characterize the pharmacokinetics of TBA in male and female F-344 rats following intravenous administration of 37.5, 75, 150 and 300 mg/kg TBA. TBA was observed to undergo a rapid distribution phase followed by a slower elimination phase. The steady-state volume of distribution for TBA was roughly 4.5 times greater than total body water, and the clearance was lower than the estimated glomerular filtration rate. The elimination of TBA appears to saturate at higher doses, as evidenced by a disproportional increase in area under the concentration-time curve and decreased rate of clearance.

Inhaled tert-butyl acetate and its metabolite tert-butyl alcohol accumulate in the blood during exposure

1. A continuous 5 h-exposure to approximately 440 ppm tert-butyl acetate in air (via a tracheal canule) resulted in continuously increasing concentrations of tert-butyl acetate and tert-butyl alcohol (metabolite of tert-butyl acetate) in the blood of rats. 2. This accumulation of tert-butyl acetate and tert-butyl alcohol was reproduced during a continuous exposure to about 900 ppm tert-butyl acetate in air over a period of 4 h and 15 min. After the inhalation approximately 50% of the blood level of tert-butyl acetate decreased within 45 min, but that of tert-butyl alcohol remained unchanged at a high level. 3. The accumulation of tert-butyl acetate and tert-butyl alcohol should be relevant for the health risk assessment at the workside.

Similar effects of ethanol and tert-butanol on amino acid concentrations in rat serum and liver

Both metabolic and nonmetabolic mechanisms have been proposed to the plasma amino acid decreasing effect of an acute ethanol load. We used tert-butanol, an alcohol that is only minimally metabolized, as a tool to explain the mechanism behind the amino acid decreasing effect of ethanol. Acute administration of tert-butanol was found to exert a decreasing effect on rat serum amino acid concentrations similar to that of ethanol, indicating that the mechanism of the amino acid decreasing effect of ethanol is primarily due to ethanol itself and not to its oxidation. Ethanol and tert-butanol also had similar effects on liver amino acid concentrations, including an increase in the glycine concentration and decrease in the concentrations of glutamate, alanine, leucine, and tyrosine.

Effects of ethanol and tertiary butanol on blood glucose levels and body temperature of rats

The mechanisms of ethanol's hyperglycemic and hypothermic effects were investigated by comparing the effects of ethanol with those of tertiary butanol. Tertiary butanol is an intoxicant like ethanol, but unlike ethanol it is only minimally metabolized. Consequently, tertiary butanol does not produce appreciable amounts of active metabolites or energy. Tertiary butanol exerts its neural effects primarily by directly altering the physico-chemical properties of nerve cell membranes. It was found that ethanol and tertiary butanol produce hyperglycemic and hypothermic effects whose magnitude and time course are nearly identical. These data suggest that the hyperglycemic and hypothermic effects of ethanol represent a primary physico-chemical effect on nerve cell membranes and are not secondary to its energy content or metabolites.

Ethanol promotes hydrolysis of 3H-labeled sialoconjugates from brain of mice in vitro

Acute administration of ethanol reportedly decreases total sialic acid in brain. Here, we tested the hypothesis in brain and liver that the decrement is due to increased hydrolysis of sialoglycoconjugates. Mouse tissue slices were pulse-labeled with N-[3H]acetyl-D-mannosamine, the precursor of sialic acid. Incorporation was linear for up to 4 hr of incubation. When the labeled slices were incubated with three concentrations of ethanol (0.1, 0.5, and 1 M) for 5 hr, labeled liver sialoconjugates were significantly affected only at 0.5 and 1 M ethanol, whereas labeled brain sialoconjugates were markedly decreased even at 100 mM ethanol. Sialidase activity decreased steadily with increasing concentration of ethanol, indicating that the increased hydrolysis was not attributable to an enhanced sialidase activity. n-Propanol and t-butanol had the same degradative effect as ethanol on sialocompounds; and 3 mM pyrazole, an inhibitor of alcohol dehydrogenase (ADH), had no effect on ethanol-induced degradation of sialocompounds. The protein/DNA ratio in liver showed a steady decrease with increasing ethanol. The data thus confirm the in vivo reports of ethanol-enhanced cleavage and rule out any increase in sialidase activity as a major cause.

Effects of ethanol and tertiary-butanol on energy expenditure and substrate utilization in the rat

The acute effects of ethanol and tertiary-butanol, an alcohol which is not metabolized via the alcohol dehydrogenase pathway, on whole body metabolism were studied using indirect calorimetry. Ethanol, but not t-butanol, increased energy expenditure in food-deprived rats. Both ethanol and t-butanol reduced respiratory quotient (RQ), an index of overall body energy substrate utilization. The lowered RQ indicates an increased dependence upon lipids as an energy source. Taken together, these data suggest that ethanol, probably within a narrow dose range, can enhance energy expenditure in the rat, either via a metabolite (e.g., acetaldehyde) or through a consequence of its oxidation. The increase in lipid mobilization seen after acute treatment with ethanol, on the other hand, appears to be independent of its oxidation.

Brain membrane disordering after acute in vivo administration of ethanol, isopropanol or t-butanol in rats

Brain synaptosomal membranes were prepared from rats sacrificed 18 hr after a single intragastric dose of water or of ethanol (100 mmol/kg), when blood ethanol had fallen almost to zero. Fluorescence polarization of DPH, and (Na+ + K+)ATPase activity, were studied in these membranes in the presence of 0, 0.175, 0.3 or 0.7 M ethanol in vitro. After in vivo ethanol, basal ATPase activity was slightly increased, membrane fluidity was unchanged, but both measures showed increased sensitivity to the effects of ethanol in vitro. Similar results were found after an equivalent in vivo dose of isopropanol, but not of t-butanol. These findings indicate that the sensitization to in vitro effects of ethanol or isopropanol, after in vivo treatment with these alcohols, is probably not dependent principally on their lipid solubilities.

Production of formaldehyde and acetone by hydroxyl-radical generating systems during the metabolism of tertiary butyl alcohol

t-Butyl alcohol is not a substrate for alcohol dehydrogenase or for the peroxidatic activity of catalase and, therefore, it is used frequently as an example of a non-metabolizable alcohol. t-Butyl alcohol is, however, a scavenger of the hydroxyl radical. The current report demonstrates that t-butyl alcohol can be oxidized to formaldehyde plus acetone by hydroxyl radicals generated from four different systems. The systems studied were: (a) two chemical systems, namely, the iron catalyzed oxidation of ascorbic acid and the Fenton reaction between H2O2 and iron; (b) an enzymatic system, the coupled oxidation of xanthine by xanthine oxidase; and (c) a membrane-bound system, NADPH-dependent microsomal electron transfer. The oxidation of t-butyl alcohol appeared to be mediated by hydroxyl radicals, or by a species with the oxidizing power of the hydroxyl radical, because the production of formaldehyde plus acetone was (a) inhibited by competing scavengers of the hydroxyl radical; (b) stimulated by the addition of iron-EDTA; and (c) inhibited by catalase. The last observation suggests that H2O2 served as the precursor of the hydroxyl radical in all three systems. A possible mechanism is hydrogen abstraction to form the alkoxyl radical [CH3)3-C-O.), spontaneous fission of the alkoxyl radical to produce acetone and the methyl radical (CH3.), interaction of the methyl radical with O2 to form the methyl peroxy radical (CH300.), and decomposition of the later to formaldehyde. These results extend the alcohol oxidizing capacity of the microsomal alcohol oxidizing system to a tertiary alcohol. Since t-butyl alcohol is not a substrate for alcohol dehydrogenase or catalase, the ability of microsomes to oxidize t-butyl alcohol lends further support for a role for hydroxyl radicals in the microsomal alcohol oxidation system. In view of the production of formaldehyde, and the reactivity as well as further metabolism of this aldehyde, caution should be used in interpreting experiments in which t-butyl alcohol is used as a presumed "non-metabolizable" alcohol. t-Butyl alcohol may be a valuable probe for the detection of hydroxyl radicals in intact cells and in vivo.

Inhibition by alcohols of the localization of radioactive nitrosonornicotine in sites of tumor formation

Oral administration of ethanol, n-butanol, or t-butanol to mice 20 minutes before injection of carbon-14-labeled nitrosonornicotine inhibited the localization of radioactivity in bronchial and salivary duct epithelium and in the liver. Localization of radioactivity in the nasal epithelium and esophagus was not significantly reduced. These alcohols therefore may selectively inhibit tumor formation in three of the five sites where this carcinogen typically acts.