[Current knowledge on gamma-hydroxybutyric acid (GHB), gamma-butyrolactone (GBL) and 1 ,4-butanediol (1,4-BD)]

Gamma-hydroxybutyric acid (GHB) is an old anaesthetic drug which was misused in the 80-90's as an anabolic agent (bodybuilding), recreational drug (drunkenness, euphoric, disinhibiting and aphrodisiac effects) and as a date rape drug (disinhibiting, hypnotic and amnesic effects). Its use in the general population is low, and mainly concerns gay population in nightclubs and young people in parties. The intoxications, above all with alcohol combination, can be severe, with coma and breathing depression, or even fatal. Chronic use leads to psychic and physical dependence; withdrawal syndrome can be severe, with agitation and delirium. In 1999, GHB classification as a narcotic resulted in the increased use of GHB prodrugs gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD), which were easily commercially available as solvent and cleaning products. Like GHB, they have a narrow window of use, and share similar toxicity. Their increased cases of recreational use and of severe drug intoxication, abuse and dependence, led the French Ministry of Health in 2011 to prohibit their sale and transfer to the public.

[Setting limit values for chemical substances in the workplace: DNEL(INH) setting according to REACH principles following the example of 2-butyne-1,4-diol]

BACKGROUND

Derived No Effect Level (DNEL(inh)) has been set for occupational exposure to but-2-yno-1,4-diol according to REACH principles. Maximum allowable concentration (MAC) and DNEL(inh) have been compared.

MATERIAL AND METHODS

Experimental data from two inhalation studies on rats and three oral studies have been used to calculate DNEL.

RESULTS

Estimated DNEL(inh) values show significant differences and fall within the range of 0.33-0.02 mg/m3, depending on the chosen experiment and critical effect. It seems that a 30-day inhalation study best reflects the penetration of xenobiotic to the human organism. This experiment has been used to set MAC value of but-2-yno-1,4-diol of 0,25 mg/m3 and it is close to local DNEL(inh)--0.10 mg/m3. Both values have been estimated on the same starting point NOAEC(loc)--0.5 mg/m3, but different assessment factors have been applied.

CONCLUSIONS

A general feeling is that because of the differences in methodologies for calculating DNELs versus those used for calculating health-based OELs, the DNEL will tend to be lower than any corresponding health-based OEL for that chemical. This indicates that the OEL does not provide the appropriate level of protection required by REACH. The calculation leads to a new value (DNEL) that requires different risk management measures and operational conditions.

The importance of 3,4-epoxy-1,2-butanediol and hydroxymethylvinyl ketone in 3-butene-1,2-diol associated mutagenicity

1,2:3,4-Diepoxybutane is hypothesized to be the main intermediate involved in mutagenicity following exposure to low levels of 1,3-butadiene (BD) in mice, while metabolites of 3-butene-1,2-diol (BD-diol) are thought to become involved in both rats and mice at higher exposures. BD-diol is biotransformed to hydroxymethylvinyl ketone (HMVK), a potentially mutagenic metabolite, and 3,4-epoxy-1,2-butanediol (EB-diol), a known mutagen. To determine the relative importance of HMVK and EB-diol in BD-diol associated mutagenesis, we have examined the dosimetry of a HMVK derived DNA adduct, as well as EB-diol derived DNA and hemoglobin adducts, in rodents exposed to BD-diol. We previously demonstrated similarities in the shapes of the dose-response curves for EB-diol derived DNA adducts, hemoglobin adducts, and Hprt mutant frequencies in BD-diol exposed rodents, indicating that EB-diol was involved in the mutagenic response associated with BD-diol exposure. To examine the role of HMVK in BD-diol mutagenicity, a method to quantify the alpha-regioisomer of HMVK derived 1,N(2)-propanodeoxyguanosine (alpha-HMVK-dGuo) was developed. The method involved enzymatic hydrolysis of DNA, HPLC purification, and adduct measurement by liquid chromatography - tandem mass spectrometry. Intra- and inter-experimental variabilities were determined to be 2.3-18.2 and 4.1%, respectively. The limit of detection was approximately 5 fmol of analyte standard injected onto the column or 5 fmol/200 microg DNA. The method was used to analyze liver DNA from control female F344 rats and female F344 rats exposed to 36 ppm BD-diol. In addition, liver samples from female Sprague-Dawley rats exposed to 1000 ppm BD were analyzed. alpha-HMVK-dGuo was not detected in any of the samples analyzed. Several possible explanations exist for the negative results including the possibility that alpha-HMVK-dGuo may be a minor adduct or may be efficiently repaired. Alternatively, HMVK itself may be readily detoxified by glutathione (GSH) conjugation. While experiments must be conducted to understand the exact mechanism(s), these results, in addition to published EB-diol derived adduct dosimetry and existing HMVK derived mercapturic acid data, suggest that EB-diol is primarily responsible for BD-diol induced mutagenicity in rodents.

A review of evidence leading to the prediction that 1,4-butanediol is not a carcinogen

1,4-Butanediol is an industrial chemical used primarily as an intermediate in the manufacture of other organic chemicals. It has recently been associated with deaths, addiction and withdrawal related to its promotion and use as a dietary supplement. The rapid absorption and conversion of 1,4-butanediol to gamma-hydroxybutyric acid (GHB, or date rape drug) in animals and humans is well documented and is the basis for its abuse potential. A disposition and metabolism study conducted in F344 rats by the National Toxicology Program (NTP) confirmed the rapid conversion of 1-(14)C-1,4-butanediol to (14)CO2. Because of this, the toxicological profile of 1,4-butanediol resembles that of gamma-hydroxybutyric acid. Gamma-hydroxybutyric acid occurs naturally in the brain and peripheral tissues and is converted to succinate and metabolized through the TCA cycle. Although the function of gamma-hydroxybutyric acid in peripheral tissues is not known, the presence of specific high affinity receptors for gamma-hydroxybutyric acid suggests that it functions as a neuromodulator in the brain and neuronal tissue. Gamma-hydroxybutyric acid readily crosses the blood-brain barrier and elicits characteristic neuropharmacologic responses after oral, i.p., or i.v. administration. The same responses are observed after administration of 1,4-butanediol. The cyclic lactone of gamma-hydroxybutyric acid, gamma-butyrolactone, is also rapidly converted to gamma-hydroxybutyric acid by enzymes in the blood and liver in animals and humans, and produces pharmacological effects identical to those produced by 1,4-butanediol and gamma-hydroxybutyric acid. Gamma-butyrolactone was previously evaluated by the NTP in 14-day and 13-week prechronic toxicology studies and in 2-year chronic toxicology and carcinogenesis studies in F344 rats and B6C3F1 mice. No organ specific toxicity occurred. In the carcinogenesis studies there was an equivocal response in male mice based on a marginal increase in the incidence of pheochromocytomas of the adrenal medulla. Because the absence of chronic toxicity and significant carcinogenicity of gamma-hydroxybutyric acid were established in NTP prechronic and chronic studies with gamma-butyrolactone, it is concluded that similar results would be obtained in a 2-year study with 1,4-butanediol, and that 1,4-butanediol is not a carcinogen.

4-Methylpyrazole Decreases 1,4-Butanediol Toxicity by Blocking Itsin VivoBiotransformation to γ-Hydroxybutyric Acid

1,4-Butanediol (1,4-BD), a prodrug converted in vivo to gamma-hydroxybutyric acid by alcohol dehydrogenase, has resulted in life-threatening overdoses and deaths. We investigated whether 4-methylpyrazole (4-MP), an alcohol dehydrogenase antagonist, can be used as an antidote in a murine model of 1,4-BD overdose. CD-1 mice were overdosed with 1,4-BD, 600 mg/kg i.p. Mice then received 4-MP, 25 mg/kg i.p., or control injections after 1 min, 5 min, and symptom appearance. Mice were then evaluated for toxicity by the righting reflex and rotarod test every 10 min after intervention. When 4-MP was administered 1 and 5 min after 1,4-BD overdose, mice completely maintained their righting reflex. Conversely, control mice lost their righting reflex for 110 and 130 min, respectively (P < 0.05). When 4-MP was administered after symptomatic 1,4-BD overdose, mice lost their righting reflex but recovered it by 60 min. Conversely, control mice lost their righting reflex and recovered it by 140 min (P < 0.05). When 4-MP was administered at 1 min after 1,4-BD overdose, mice never failed the rotarod test. Conversely, control mice failed the rotarod test for 210 min (P < 0.05). When 4-MP was administered 5 min after 1,4-BD and after symptomatic 1,4-BD overdose, mice failed the rotarod test for 100 and 110 min, respectively. Conversely, control mice failed the rotarod test for 210 and 180 min, respectively (P < 0.05). In addition, treatment of mice with 4-MP significantly attenuated increases in blood gamma-hydroxybutyric acid concentrations and prevented loss of the righting reflex and failure of the rotarod test. In this murine model of 1,4-BD overdose, 4-MP conferred antidotal effects by inhibiting alcohol dehydrogenase-mediated biotransformation of 1,4-BD to gamma-hydroxybutyric acid.

??-Butyrolactone and 1,4-Butanediol

gamma-Hydroxybutyrate (GHB) is a GABA-active CNS depressant, commonly used as a drug of abuse. In the early 1990s, the US Drug Enforcement Administration (DEA) warned against the use of GHB and restricted its sale. This diminished availability of GHB caused a shift toward GHB analogues such as gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) as precursors and surrogates. Both GBL and 1,4-BD are metabolically converted to GHB. Furthermore, GBL is commonly used as a starting material for chemical conversion to GHB. As such, the clinical presentation and management of GBL and 1,4-BD intoxication shares a great deal of common ground with that for GHB. This similarity exists not only for acute intoxication but also for withdrawal in those patients with a history of extended high-dose abuse. This review examines the history of GHB analogue abuse as well as the clinical presentation and management of acute intoxication and withdrawal associated with abuse of these compounds.

Aquatic toxicity of selected chemicals as a basic criterion for environmental classification

In order to protect public health and the environment, the EU legislation has proposed a classification of dangerous substances. Chemicals are classified according to physico-chemical as well as toxicological and ecotoxicological properties. Environmental classification is based on inherent harmful potential of a substance to organisms and on its environmental fate, that is, degradation and bioaccumulation potential. In this study, experimental data on acute and chronic toxicity to aquatic organisms and biodegradability and bioaccumulation data obtained from literature were used to classify arsenic (applied as As2O3), copper (applied as CuCl2), phenol and 1,4-butynediol. For this purpose, the "base set data" obtained from standardised test methods served as a convenient indicator of the inherent toxicity of tested chemicals. Additional data about environmentally relevant properties of arsenic and 1,4-butynediol could lead to a revision of present chemical classification and labelling.

Electromagnetic re-warming of cryopreserved tissues: effect of choice of cryoprotectant and sample shape on uniformity of heating

A method that has been proposed for the cryopreservation of tissues and organs is to add a cryoprotective agent (CPA) in sufficient concentration to allow vitrification, and to use rapid electromagnetic heating to prevent the formation of ice crystals during the re-warming. We have compared the physical and biological properties of four CPAs, measuring the speed and uniformity of heating in a 36 mm sphere placed in a 434 MHz applicator, and the toxicity to ECV304 endothelial cells. Ethanediol and dimethyl sulfoxide were found to be suitable for rapid, uniform heating but toxic to the endothelial cells at vitrifying concentrations. Butane-2,3-diol was less toxic, but the heating patterns were unacceptably non-uniform. Propane-1,2-diol was not significantly more toxic than butane-2,3-diol, and did allow uniform heating. It is therefore the best choice of CPA for the vitrification of tissues. We have shown that the uniformity of heating correlates with the dielectric properties of the perfusate. Furthermore, we have shown that uniform heating is feasible in non-spherical samples provided they are approximately ellipsoidal.

Pretreatment of CD-1 mice with 4-methylpyrazole blocks toxicity from the gamma-hydroxybutyrate precursor, 1,4-butanediol

1,4-Butanediol (1,4-BD) is the dihydroxy precursor of gamma-hydroxybutyrate (GHB), a popular recreational drug that has been banned by the United States Food and Drug Administration (FDA) and controlled as a federal schedule I drug. 1,4-BD is enzymatically converted in vivo to GHB by alcohol dehydrogenase (ADH), and overdoses can result in coma, severe respiratory depression, bradycardia, hypothermia, seizures, and death. Presently, there is no antidote. We pretreated CD-1 mice with the ADH antagonist, 4-methylpyrazole (4-MP), to determine if blocking ADH can prevent or decrease toxicity from 1,4-BD overdose. Pretreatment with 4-MP increased the Toxic Dose-50 (TD(50)) of 1,4-BD for the righting reflex from 585 mg/kg (95% CI, 484-707 mg/kg) in control mice to 5,550 mg/kg (95% CI, 5,353-5,756 mg/kg) in pretreated mice. Pretreatment with 4-MP also increased the TD(50) of 1,4-BD for the rotarod test from 163 mg/kg (95% CI, 136-196 mg/kg) in control mice to 4,900 mg/kg (95% CI, 4,812-4,989 mg/kg) in pretreated mice. Pretreatment with 4-MP significantly decreased the toxicity of 1,4-BD in CD-1 mice, presumably by inhibiting its ADH biotransformation to GHB. 4-MP warrants further investigation as a potential antidote for this increasingly abused drug.

Enzyme and receptor antagonists for preventing toxicity from the gamma-hydroxybutyric acid precursor 1,4-butanediol in CD-1 mice

1,4-Butanediol (1,4-BD), the diol alcohol precursor of gamma-hydroxybutyric acid (GHB), undergoes in vivo enzymatic biotransformation to GHB by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase. The subsequent metabolite, GHB, is pharmacologically active at GABA(B) and GHB receptors. GHB can be metabolized in vivo to gamma-aminobutyric acid (GABA) and trans-4-hydroxycrotonic acid (T-HCA), which are also pharmacologically active at GABA(B) receptors and GHB receptors, respectively. Therefore, we speculate that 1,4-BD overdose toxicity can be prevented or attenuated with the ADH enzyme inhibitor 4-methylpyrazole (4-MP) as well as with CGP-35348 and NCS-382, novel high-affinity receptor antagonists of GABA(B) receptors and GHB receptors, respectively. In our murine model of acute 1,4-BD overdose, pretreatment of CD-1 mice with 4-MP significantly attenuated increases in blood GHB concentrations and prevented loss of the righting reflex and failure of the rotarod test. Also, pretreatment with CGP-35348 and its combination with NCS-382 significantly decreased the duration of failure for the rotarod test and the percentage of animals failing the rotarod test, respectively. However, pretreatment of CD-1 mice with NCS-382 alone produced prolonged failure of the rotarod test, an unexpected synergistic effect with 1,4-BD and presumably GHB, which has not previously been demonstrated.

Vitrification media: toxicity, permeability, and dielectric properties

The aim of this study was to select a cryoprotectant for use in attempts to preserve tissues and organs by vitrification. The first step was to select a cell line with which to compare the toxicity of a range of commonly used cryoprotectants. An immortal vascular endothelial cell (ECV304) was exposed to vitrifying concentrations of four cryoprotectants: dimethyl sulfoxide (Me(2)SO; 45% w/w); 2,3 butanediol (BD; 32%); 1,2-propanediol (PD; 45%); and ethanediol (ED; 45%). Three times of exposure (1, 3, and 9 min) and two temperatures (22 and 2-4 degrees C) were studied. After removal of the cryoprotectant, the ability of the cells to adhere and divide in culture over a 2-day period was measured and expressed as a Cell Survival Index (CSI). There was no measurable loss of cells after exposure to the four cryoprotectants but 3-min exposure to BD, PD, or Me(2)SO at room temperature completely destroyed the ability of the cells to adhere and divide in culture. In contrast, exposure to all four cryoprotectants at 2-4 degrees C for up to 9 min permitted the retention of significant cell function, the CSIs, as a proportion of control, being 76.3+/-7.0% for BD, 63.6+/-7.1% for PD, 37.0+/-4.1 for Me(2)SO, and 33.2+/-3.0 for ED. The permeability properties of the cells for these four cryoprotectants was also measured at each temperature. Permeability to water was high, L(p) approximately equal 10(-7) cm/s/atm at 2-4 degrees C with all the cryoprotectants, but there were substantial differences in solute permeability: BD and PD were the most permeable at 2-4 degrees C (P(s)=4.1 and 3.0 x 10(-6) cm/s, respectively). Equilibration of intracellular cryoprotectant concentration was rapid, due in part to high water permeability; the cells were approximately 80% of their physiological volume after 10 min. Treatment at 2-4 degrees C with BD was the least damaging, but PD was not significantly worse. Exposure to vitrifying concentrations of ED and Me(2)SO, even at 2-4 degrees C, was severely damaging. Segments of rabbit carotid artery were treated with vitrifying concentrations of each of the two most favorable cryoprotectants, BD and PD, for 9 min. It was shown that each cryoprotectant reduced smooth muscle maximum contractility to a similar extent and abolished the acetylcholine response. However, vital staining revealed that exposure to BD also caused substantial damage to the endothelial lining, whereas the endothelium was completely intact after PD exposure, raising the possibility that the effect of PD on NO release may be reversible. In later stages of this project it is planned to use dielectric heating to rewarm the tissues and thereby avoid devitrification. The effects of each cryoprotectant on this mode of heating was therefore studied. Gelatin spheres containing vitrifiable concentrations of each cryoprotectant were rewarmed from -60 degrees C in a radiofrequency applicator. Because the uniformity of heating is related to the dielectric properties of the material, these properties were also measured. PD was the most suitable. These physical measurements, combined with the measurements of toxicity and permeability, indicate that PD is the most favorable cryoprotectant of those tested for use in subsequent stages of this study.

Alcohol-related diols cause acute insulin resistance in vivo

Epidemiological studies suggest that alcohol consumption is an independent risk factor for the development of non-insulin-dependent diabetes mellitus (NIDDM). Alcoholism is known to be associated with increased plasma levels of two novel diols, 2,3-butanediol and 1,2-propanediol, metabolites known to impair insulin action in isolated adipocytes. This study examines whether 2,3-butanediol and 1,2-propanediol have the capacity to impair insulin action acutely in vivo in the rat. Using the euglycemic-hyperinsulinemic clamp, it is shown that the two diols reduce whole-body glucose utilization (by approximately 30%), with the onset of insulin resistance in vivo occurring at plasma concentrations of 2,3-butanediol (33 micromol/L) at least one order of magnitude (P < .001) lower than 1,2-propanediol (432 micromol/L). Tracer methodologies using [U-14C]glucose and 2-deoxy[1-(3)H]glucose indicate that the reduction in whole-body glucose utilization is accompanied by a reduction in glucose uptake and glycogen synthesis in the skeletal muscle and heart. The association between elevated plasma diol levels and insulin resistance demonstrated in this report raises the question of whether there is a link between the high plasma diol levels in alcohol abusers and their increased susceptibility to NIDDM.

Studies on the genotoxicity of the mammalian lignans enterolactone and enterodiol and their metabolic precursors at various endpoints in vitro

The mammalian lignans enterolactone (ENL) and enterodiol (END) are formed by intestinal bacteria from the plant lignans matairesinol (MAT) and secoisolariciersinol (SEC), respectively, which are ingested with different types of food. ENL and END are weak estrogens. According to epidemiological and biochemical studies, lignans may act as anticarcinogens, but little is known about their genotoxic potential. We have therefore investigated the effects of ENL, END, MAT and SEC on cell-free microtubule assembly and at the following genetic endpoints in cultured male Chinese hamster V79 cells: disruption of the cytoplasmic microtubule complex, induction of mitotic arrest, induction of micronuclei and their characterization by CREST staining, and mutagenicity at the HPRT gene locus. The lignans were tested at concentrations of 200 microM in the cell-free system and 100 microM in cultured cells, which represents the limit of solubility in each assay. The established aneuploidogen diethylstilbestrol and the clastogen 4-nitroquinoline-N-oxide were used as positive reference compounds. As none of the four lignans had any activity at the endpoints studied, we conclude that ENL, END, MAT and SEC are devoid of aneuploidogenic and clastogenic potential under the experimental conditions used in this study.

Developmental toxicity of 2-butin-1,4-diol following oral administration to the rat

Developmental toxicity of 2-butin-1,4-diol was determined in groups of 18-22 pregnant Wistar rats at dose levels of 10, 40 and 80 mg/kg bw/day administered by gavage from days 6 to 15 pc. At 80 mg/kg bw/day food consumption and maternal body weight were reduced and one dam died during the treatment period. At this dose level the incidence of affected fetuses per litter with accessory 14th ribs was increased. This variation is assessed as an embryotoxic effect resulting from non-specific stress on the dams. No teratogenic effects were caused by 2-butin-1,4-diol. The NOAEL on the maternal and the developing organism was 40 mg/kg bw/day.

The influence of flaxseed and lignans on colon carcinogenesis and beta-glucuronidase activity

Flaxseed, the richest source of mammalian lignan precursors, such as secoisolariciresinol diglycoside (SD), has been shown over the short term to decrease some early markers of colon cancer risk. This study determined whether over the long term flaxseed still exerts a colon cancer protective effect, whether its effect may, in part, be due to its high content of SD and whether any change in beta-glucuronidase activity plays a role in the protective effect. Six groups of male Sprague-Dawley rats were fed for 100 days either a basal high fat (20%) diet (BD), BD supplemented with 2.5 or 5% flaxseed or 2.5 or 5% defatted flaxseed (equivalent to the respective flaxseed diets) or BD with a daily gavage of 1.5 mg SD. All rats were injected with a single dose of azoxymethane (15 mg/kg body wt) 1 week prior to commencing the dietary treatments. Urinary lignan excretion, which is an indicator of mammalian lignan production, was significantly increased in the flaxseed and defatted flaxseed groups. The total activity of cecal beta-glucuronidase was significantly increased in a dose-dependent manner by the flaxseed and defatted flaxseed diet groups. Compared with the control the number of aberrant crypts per focus was significantly reduced in the distal colon of the treated rats. Four microadenomas and two polyps were observed in the control group, but not in the treated groups. The total activity of beta-glucuronidase was positively correlated with total urinary lignan excretion and negatively with the total number of aberrant crypts and the total number of aberrant crypt foci in the distal colon. There were no significant differences between the flaxseed and the corresponding defatted flaxseed groups. It is concluded that flaxseed has a colon cancer protective effect, that it is due, in part, to SD and that the protective effect of flaxseed is associated with increased beta-glucuronidase activity.

NTP summary report on the metabolism, disposition, and toxicity of 1,4-butanediol (CAS No. 110-63-4)

1,4-Butanediol is an industrial chemical used in the manufacture of other organic chemicals. It was nominated by the National Cancer Institute and selected for evaluation by the NTP because of high production volume, the potential for worker exposure, the lack of adequate toxicological characterization, and the lack of evaluation for carcinogenic potential. As documented in the scientific literature, 1,4-butanediol is rapidly absorbed and metabolized to gamma-hydroxybutyric acid in animals and humans. A metabolism and disposition study conducted in F344/N rats by the NTP confirmed the rapid and extensive conversion of 1-[14C]-1,4-butanediol to 14CO2. Because of this rapid and extensive conversion, the toxicological profile of 1,4-butanediol reflects that of gamma-hydroxybutyric acid. gamma-Hydroxybutyric acid is a naturally occurring chemical found in the brain and peripheral tissues which is converted to succinate and processed through the tricarboxylic acid cycle. Although the function of gamma-hydroxybutyric acid in peripheral tissues is unknown, in the brain and neuronal tissue it is thought to function as a neuromodulator. gamma-Hydroxybutyric acid readily crosses the blood-brain barrier, and oral, intraperitoneal, or intravenous administration elicits characteristic neuropharmacologic responses. These same responses are observed after administration of 1,4-butanediol. The lactone of gamma-hydroxybutyric acid, gamma-butyrolactone, is also rapidly converted to gamma-hydroxybutyric acid by enzymes in the blood and liver of animals and humans. gamma-Butyrolactone was previously evaluated by the NTP in 14-day and 13-week toxicology studies and 2-year toxicology and carcinogenesis studies in F344/N rats and B6C3F1 mice. No organ-specific toxicity occurred in the toxicology studies. In the carcinogenesis studies, an equivocal response occurred in male mice, based on a marginal increase in the incidence of pheochromocytomas of the renal medulla. Because of the rapid and extensive conversion of gamma-butyrolactone to gamma-hydroxybutyric acid, the evaluation of gamma-butyrolactone was in fact an evaluation of gamma-hydroxybutyric acid. This summary report presents a review of the current literature which documents that both 1,4-butanediol and gamma-butyrolactone are rapidly metabolized to gamma-hydroxybutyric acid, and the pharmacologic and toxicologic responses to these chemicals are due to their metabolic conversion to gamma-hydroxybutyric acid. Because the toxicity and carcinogenicity of gamma-hydroxybutyric acid was fully evaluated in the NTP studies of gamma-butyrolactone, and a lack of organ-specific toxicity or carcinogenic potential was demonstrated, it is concluded that there is a high likelihood that 1,4-butanediol would be negative in a similar set of studies. For these reasons, it is the opinion of the NTP that 1,4-butanediol should be considered not carcinogenic in animals and no further evaluation of 1,4-butanediol is needed at this time.

Liver preservation below 0 degrees C with UW solution and 2,3-butanediol

Long-term preservation of the liver is needed to transform liver transplantation from an emergency operation to an elective procedure and therefore to improve the results of liver transplantation. We explored the possibility of extending the cold ischemia time of the rat liver by using a preservation temperature below 0 degrees C together with the addition of a cryoprotective agent (2,3-butanediol) at a low concentration in the preservation solution. Rat livers were preserved for 72 h either with UW solution at +4 degrees C (group 1) or with a UW solution, to which 2,3-butanediol at 8% (at +4 degrees C (group 2) or at -4 degrees C (group 3, experimental group)) was added. Following the preservation process, the viability of the livers was assessed using the isolated perfused liver model. Enzymatic release, bile production, and portal venous flow were not significantly different between group 1 and group 3. In the two groups in which preservation included 2,3-butanediol, the enzymatic release was significantly greater when the preservation temperature was +4 degrees C. We conclude that, using this method, preservation of the rat liver below 0 degrees C seems feasible. However, despite its low concentration, some toxicity of 2, 3-butanediol was suspected. This would counterbalance the benefit resulting from the temperature-related decrease of the enzymatic activities involved in cold ischemia damage. The potential advantages of this method need to be confirmed by assessing liver viability using a liver transplantation model.

Effect of D- and L-1,3-butanediol isomers on glycolytic and citric acid cycle intermediates in the rat brain

DL-1,3-butanediol (DL-BD) is an ethanol dimer which affords cerebral protection in various experimental models of hypoxia and ischemia but its mechanism of action is unknown. DL-BD is a ketogenic alcohol and it has been proposed that its protective effect was accomplished through cerebral utilization of ketone bodies. Since DL-BD is a racemic, its metabolic effects could be due to D, L or both isomers. The effects of equimolar doses of DL-, D- and L-BD (25 mmol/Kg) on cerebral metabolism were studied by measuring the cortical levels of the main glycolytic (glycogen, glucose, glucose 6-phosphate, fructose 1,6-diphosphate, pyruvate and lactate) and citric acid cycle (citrate, alpha-ketoglutarate and L-malate) intermediates. The two BD isomers exerted different effects on cerebral metabolism. Unlike L-BD, D- and DL-BD treatments resulted in a slight (+10%) but significant increase in citrate level whereas L-BD treatment led to significant reduction in pyruvate (-12%) and lactate (-24%) levels. These effects were apparently not linked to hyperketonemia, since DL-BHB treatment, which mimicked hyperketonemia induced by DL-BD, had no effect on cerebral metabolites but might be due to intracerebral metabolism of BD.

Reduction in toxicity for red blood cells in buffered solutions containing high concentrations of 2,3-butanediol by trehalose, sucrose, sorbitol, or mannitol

Erythrocytes were stored at 4 degrees C in solutions of phosphate-buffered saline containing 2,3-butanediol and 4% (w/w) trehalose, sucrose, sorbitol, or mannitol. The 2,3-butanediol contained 96.7% (w/w) racemic mixture of the levo and dextro isomers and only 3.1% (w/w) of the meso isomer (2,3-butanediol 97% dl). The concentrations of 2,3-butanediol were 30 and 35% (w/w). A solution of 30% 2,3-butanediol showed relatively low toxicity. Hemolysis was only 2% after 5 h, but increased to 6% after 21 h and reached 60% after 46 h. Adding 4% (w/w) of one of the above compounds drastically decreased the toxicity. The two most efficient were the sugars trehalose and sucrose. With 30% 2,3-butanediol and 4% of any of the four compounds, hemolysis was about 0.6% after 2 days of storage. Furthermore, with trehalose or sucrose, hemolysis remained below 3% for 1 month. With sorbitol or mannitol, hemolysis slowly increased to 2% after 7 days and then increased rapidly. Even with 35% 2,3-butanediol, solutions containing trehalose or sucrose showed low toxicity. Hemolysis was also measured after redilution to buffered solution without 2,3-butanediol and without the additive, to mimic perfusion of organs with cryoprotectants and washing. Minima of hemolysis were observed after a few days of storage. The present solutions also have high glass-forming tendencies. They could be of great interest for organ vitrification.

Chemical mutagenesis testing in Drosophila. IX. Results of 50 coded compounds tested for the National Toxicology Program

Fifty chemicals were tested for mutagenic activity in post-meiotic and meiotic germ cells of male Drosophila melanogaster using the sex-linked recessive lethal (SLRL) assay. As in the previous studies in this series, feeding was chosen as the first route of administration. If the compound failed to induce mutations by this route, injection exposure was used. One gaseous chemical (1,3-butadiene) was tested only by inhalation. Those chemicals that were mutagenic in the sex-linked recessive lethal assay were further tested for the ability to induce reciprocal translocations. Eleven of the 50 chemicals tested were mutagenic in the SLRL assay. These included bis(2-chloroethyl) ether, 1,4-butanediol diglycidyl ether, 1-chloro-2-propanol, dimethyl methylphosphonate, dimethyl morpholinophosphoramidate, dimethyloldihydroxyethylene urea, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isatin-5-sulfonic acid (Na salt), isopropyl glycidyl ether, and urethane. Five of these, including 1,4-butanediol diglycidyl ether, 2,2-dimethyl vinyl chloride, hexamethylphosphoramide, isopropyl glycidyl ether, and urethane, also induced reciprocal translocations.

Successful cryopreservation of mouse blastocysts using a new vitrification solution

Mouse blastocysts were exposed to solutions containing four concentrations (10, 20, 30 and 40% v/v) of six permeating cryoprotectants (glycerol, ethylene glycol, propylene glycol, dimethyl sulfoxide, 1,3-butanediol and 2,3-butanediol) in phosphate-buffered saline (PBS) with calf serum (CS) at room temperature (20-22 degrees C). Blastocysts were exposed to these solutions for various periods, diluted into PBS plus CS with or without 1 mol trehalose l-1 solution and their subsequent survival in vitro was examined. Two-way anova showed a significant interaction (P < 0.01) between cryoprotectant type, concentration of cryoprotectant and method of dilution. However, no significant interaction was observed between cryoprotectant type and duration of exposure. Results suggest that cryoprotectant-induced injury to nonfrozen blastocysts is variable and depends on the cryoprotectant used. On the basis of toxicity assays, ethylene glycol was the least harmful and was combined with dimethyl sulfoxide and 1,3-butanediol to produce a new vitrification solution. Mouse blastocysts were successfully cryopreserved using a vitrification solution (designated as VSv) consisting of 20% ethylene glycol, 20% dimethyl sulfoxide and 10% 1,3-butanediol (v/v). Embryos were equilibrated in two steps, first in an equilibration solution (designated as ESv: 10% ethylene glycol, 10% dimethyl sulfoxide and 5% 1,3-butanediol; v/v) and then to VSv or one-step in VSv at different exposure times at room temperature, and then vitrified by direct plunging into liquid nitrogen. High developmental rates were obtained in vitro when the embryos were exposed to ESv and VSv for 3 and 0.5 min, respectively (96.2%) or exposed to VSv for 0.5 min (95.4%). Prolonged exposure time proved detrimental to subsequent embryo development in vitro. When vitrified warmed embryos were transferred immediately to pseudopregnant recipients, the rate of development to normal fetuses did not significantly differ from that of the nonvitrified control (two-step, 54.2 and one-step, 45.0 versus 60.0%, P > 0.05). These results suggest that the simple vitrification solution described in this study is effective for the cryopreservation of mouse blastocysts.

Acute toxicity of 2-butyne-1,4-diol in laboratory animals

Acute toxicity of 2-butyne-1,4-diol (BYD) was evaluated in laboratory animals. The evaluation involved acute oral and dermal toxicity in rats, dermal and ocular irritation in rabbits and skin sensitization in guinea pigs. The oral LD50 values for BYD were 132 mg kg-1 in male rats and 176 mg kg-1 in female rats. Post-mortem histology showed severe damage in lungs, liver and kidneys. In surviving rats, moderate to severe degenerative changes were observed in the liver but only mild lesions in the kidneys. In acute dermal toxicity studies the test chemical was applied either as a solid substance or as 40% aqueous solution at a dose of 5 g kg-1 for 24 h. Within 48 h of application of the diluted test material, half of the rats died. Liver and kidneys were the primary targets and different stages of degeneration, including necrosis, were observed. No deaths occurred after application of the solid substance. In rabbits, BYD was slightly irritant to skin and eyes. No allergic contact dermatitis was observed in guinea pigs.

Subacute oral toxicity of 2-butyne-1,4-diol in rats

2-Butyne-1,4-diol was given to male and female Wistar Imp:DAK rats by oral gavage for 28 consecutive days in daily doses of 1, 10 or 50 mg kg-1 day-1. After 28 days all animals were necropsied. Blood samples were obtained and selected organs were weighed and prepared for histological examination. Treatment-related effects in the high-dose group consisted of: fatal cases in both sexes; depressed body weight gain in males; increase of absolute and/or relative weights of liver and kidneys in both sexes; decreased red blood cell count, haematocrit value and haemoglobin concentration in female rats and elevated reticulocyte count and leukocyte count in both sexes; increased total serum protein content in females, elevated glucose concentration in males and higher activity of sorbitol dehydrogenase in both sexes; and histopathological evidence of hepatotoxicity and nephrotoxicity in decedents, and hepatic and splenic changes in survivors. Minor hepatic, splenic and erythrocytic changes were also found in some females given the middle dose. The dose of 1 mg kg-1 day-1 was considered to be the no-observed-effect level (NOEL), and 10 mg kg-1 day-1 the lowest-observed-effect level (LOEL).

The toxicokinetics of 1,3-butylene glycol versus ethanol in the treatment of ethylene glycol poisoning

Ethylene glycol (EG) is a toxic chemical found in antifreeze and heat exchangers. Standard therapy for EG intoxication in administration of ethanol (ETOH) to inhibit its metabolism by alcohol dehydrogenase (ADH). Studies indicate 1,3-butylene glycol (BG) binds to ADH more efficiently than EG and is orally less toxic than EG or ETOH. Male rats were divided into 5 groups of 6 animals. Groups received by oral intubation a single dose of EG (32 mmole/kg), BG (39 mmole/kg) initially and every 6 h up to 72 h, ETOH (39 mmole/kg) initially and every 6 h up to 72 h, or EG initially and then either BG or ETOH every 6 h up to 72 h. Administration of ETOH produced hepatotoxicity and pulmonary pathology as indicated by changes in clinical chemistry, urinalysis, and histopathology, while BG did not. Neither ETOH nor BG produced any apparent nephrotoxicity. ETOH produced ataxia, lethargy and central nervous system depression while BG did not. BG produced a higher concentration of urinary EG indicating a better inhibition of ADH metabolism of EG. Ethanol produced a higher EG blood concentration than BG. Ethanol's higher EG blood concentration may be partially attributed to dehydration and a decreased urine output as well as inhibition of ADH metabolism. Ethanol produced mortality in all animals prior to 72 h. The EG/ETOH combination produced mortality more quickly due to additive toxicity of the combination. Lack of any significant toxicity produced by BG and the production of significant toxicities by ETOH indicates that BG is potentially a better antidote than ETOH.

Effect of 1,3-butanediol on rat liver microsomal NDMA demethylation and other monooxygenase activities

The administration of 1,3-butanediol (BD) previously has been shown to elevate blood concentrations of ketone bodies, to potentiate carbon tetrachloride hepatotoxicity, and to increase the hepatic microsomal content of cytochrome P450 and the activity of aniline hydroxylase. In the present study, oral treatment (10 g/kg) with racemic BD and each of its enantiomers (R-BD and S-BD) induced NDMA demethylase activity by approx. 1.5-fold in rat hepatic microsomes obtained 12 h later, suggesting an induction of P450IIE1, the acetone/ethanol-inducible form of P450. The results agreed with an immunochemically determined increase in the levels of this isozyme. No change in P450 content, NADPH-cytochrome-c reductase, or in pentoxyresorufin dealkylase activity were detected. Blood levels of acetone were determined during a 10-h period after BD administration and showed a higher initial rate of increase by R-BD, possibly due to steroselective metabolic oxidative metabolism. However, no difference in the induction of NDMA demethylase activity by the enantiomers could be detected. Induction of P450IIE1 probably contributes to the previously described potentiation of haloalkane-induced hepatotoxicity by BD administration.

Potentiation of CCl4-induced liver injury by ketonic and ketogenic compounds: role of the CCl4 dose

Potentiation of haloalkane hepatotoxicity by ketones and ketogenic agents is a well-known phenomenon. The importance of the CCl4 dosage in these combinations, however, has not been explored. Its influence was investigated in male Sprague-Dawley rats. Dose-effect curves for potentiation were generated using 1,3-butanediol, methyl n-butyl ketone or methyl isobutyl ketone as potentiation agents. Animals were orally treated with these compounds prior to a challenge of CCl4 (0 to 0.5 ml/kg, ip). Liver injury was assessed by monitoring plasma ALT activity and bilirubin concentrations after CCl4 treatment. The minimal effective dosage (MED) for each potentiator was used as the criterion of comparison for each combination. The MED values were determined from the plasma ALT data. Results showed that when the CCl4 dosage was increased from 0.01 to 0.10 ml/kg, the MED of each potentiator decreased 10-fold. For a given potentiator, the product of the CCl4 dosage (H, "hepatotoxicant") by the corresponding MED value (P, "potentiator") remained the same in this range of CCL4 dosages. The severity of the liver injury was similar. These findings suggest that a given level of liver injury induced by a ketone/haloalkane combination could be evaluated on the basis of the [P X H] product.

1,3-Butanediol-induced increases in ketone bodies and potentiation of CCl4 hepatotoxicity

Evidence previously reported suggest that 1,3-butanediol (BD) enhances the hepatotoxic effect of a single small dose of carbon tetrachloride (CCl4) in a dose-related manner. The present study provides additional information concerning the quantitative relationship between the severity of the ketotic state produced by BD and the magnitude of the potentiation observed and emphasizes the use of ketone bodies (KB) to predict the potential hazard of the BD-CCl4 interaction. Liver damage was modulated in male Sprague-Dawley rats by varying the concentration of the BD solutions ingested prior to a CCl4 challenge (0.1 ml/kg, i.p.). These data were compared to ketone bodies in plasma, hepatic tissue and urine. BD produced a dose-dependent metabolic ketosis observable at dosages between 1.1 and 9.9 g/kg per day given for 7 days. Plasma and liver data correlated well together. Concomitantly, potentiation of the CCl4-induced liver injury was also dose-related for the same dosage range; the minimum effective dosage of BD for potentiation was estimated as 1.1 g/kg per day. The linear correlations between hepatic or plasma KB values and the indices of hepatic dysfunction (ALT, OCT) were highly significant. Using a semiquantitative method, a correlation was also found for the urinary KB data. These results suggest that plasma KB concentrations might be useful for predicting possible potentiation of the hepatonecrotic effect of CCl4 by BD.

Ethanol potentiates the toxic effects of 1,4-butanediol

The simultaneous administration of ethanol increases the mortality rate and tissue damage observed in rats after 1,4-butanediol (1,4-BD). A related increase in tissue 1,4-BD concentration supported the hypothesis of an in vivo competition of the two substances for alcohol dehydrogenase. The clinical implications of the results, in light of the recent discovery of the presence of endogenous 1,4-BD in humans are discussed.

The effects of acetaldehyde and 2,3-butanediol on rat embryos developing in vitro

The embryotoxicity of two ethanol metabolites, acetaldehyde and 2,3-butanediol, have been examined in cultured 10-day Albino Wistar rat embryos over a 2-day period. At acetaldehyde concentrations of 100 and 260 microM, no significant effects were observed on embryonic protein, DNA, somite development, gross morphology, or viability. 800 microM was overtly toxic causing rapid death and necrosis. 2,3-butanediol at a culture medium concentration of 25 mM had no effect on any of the above parameters. The significance of these results in relation to other animal experiments with these compounds and possible ramifications regarding the aetiology of the human Fetal Alcohol Syndrome are discussed.

Reproduction and teratology study of 1,3-butanediol in rats

The effect of 1,3-butanediol on reproductive performance as well as its teratogenic, dominant lethal and cytogenetic effects were studied in five generations of Wistar rats. Animals of both sexes were fed either control diet or diet supplemented with 1,3-butanediol at dose levels of 5, 10 or 24% of the diet by weight. Reproduction and lactation parameters were comparative to controls for four of five generations of dams and pups. In contrast, the pregnancy rate of F1A rats decreased during five successive mating cycles; no pups were obtained in the high-dose level group of the fifth series of litters (F2E generation). Excluding this group, the viability of F2 generation pups revealed no significant differences between litters or between control and test groups. No definitive dose-related teratological findings were found in either soft or skeletal tissue examinations of F3B generation rats. However, incomplete ossification of sternebrae occurred frequently in mid- and high-dose fetuses, whereas missing sternebrae were noted especially in high-level fetuses. Both skeletal tissue findings suggest slight delayed fetal growth. For the dominant lethal assay of the F1B generation, the mutagenic index (percentage resorptions per implant sites) revealed no dose-related trend. In the three-generation cytogenetic study, no 1,3-butanediol related chromosomal aberrations were noted.

Carcinostatic effect of aliphatic aldehydes and aldehyde dehydrogenase activity in Ehrlich carcinoma, Sarcoma 180, and Yoshida AH 130 hepatoma

The antitumor activity of 2,3-dihydroxybutyraldehyde on Ehrlich carcinoma, Sarcoma 180, and Yoshida AH 130 hepatoma, as well as the aldehyde dehydrogenase activity in these tumors, was studied. 2,3-Dihydroxybutyraldehyde at nontoxic doses (500 mg/kg body weight i.p. daily for 7 days) slowed down the growth of solid and ascites tumors in mice. The treatment completely prevented the development of Yoshida ascites hepatoma in several rats. 2,3-Dihydroxybutyraldehyde, although it did not influence the growth of Ehrlich carcinoma transplanted in the brain of mice, significantly decreased in the lungs of these animals the number of viable tumour cells that derived from the primary tumor. All the tested tumors, which were sensitive to the action of 2,3-dihydroxybutyraldehyde, were virtually devoid of aldehyde dehydrogenase activity. These results suggest a possible relationship between the lack of this enzyme activity and the antitumor activity of aliphatic aldehydes.

Suppression by 1,3-butanediol of the ethanol withdrawal syndrome in rats

1,3-Butanediol was tested for its ability to suppress an ethanol with drawal syndrome. Male Sprague-Dawley rats were rendered physically dependent on ethanol by intragastric administration of ethanol at a dosage of 9 to 15 grams per kilogram per day over a 4-day period. A nonintoxicating oral dose of 1,3-butanediol at 4 grams per kilogram administered after elimination of ethanol from the blood was effective against the tremulous and conbulsive components of the ethanol withdrawal syndrome in all animals for 1 to 5 hours. This period coincided with the time of maximum severity of the withdrawal syndrome, as seen in the control animals.

Nutritional application and implication of 1,3-butanediol

Research in the United States on synthetic sources of dietary calories was initiated in 1958 to develop high nutrient density food for extended manned space travel. Of many known compounds screened, 1,3-butanediol was the most promising. Small amounts in ester form with fatty acids exist in nature, and tests indicate a low acute oral and chronic toxicity similar to that of propylene glycol or glycerol. Multi-generation reproduction, teratological, and mutagen studies have revealed nothing detrimental. Following an adaptation period, 1,3-butanediol furnishes approximately 6 kcal/g if fed at levels not exceeding 20% in the diet of rats. Higher levels result in an impairment in growth and food utilization. In young animals, body fat stores appear to be lessened, as is resistance to the stress of extreme cold. However, dogs fed 20% 1,3-butanediol can maintain sustained muscular work on treadmills, but larger amounts can result in incoordination due to a narcotic effect common to glycols. Little research has been conducted on the behavioral effects of large doses. At present, 1,3-butanediol is used mainly as a solvent for food flavors. If the unpleasant taste problem can be overcome and if given FDA approval, 1,3-butanediol may have an increased role in our food supply as a functional food additive, preservative, and source of calories for man and animals.