Cigarette smoke extract and isoprene resulted in the induction of apoptosis and autophagy in human placenta choriocarcinoma JEG-3 cells

In this study, the effects of cigarette smoke (CS) on the induction of apoptosis via reactive oxygen species (ROS) production and endoplasmic reticulum stress (ER stress) of JEG-3 human choriocarcinoma cells were examined to confirm the relationship between CS and placenta development. Upon TUNEL assay, CS extract (3R4F; 0.3 and 2.1 μM) increased JEG-3 apoptosis. Western blot assay revealed that the protein expressions of p53, Bax, and CCAAT-enhancer-binding protein homologous protein (CHOP) increased, while the levels of Bcl-2 were reduced following CS extract treatment. Moreover, 2',7'-dichlorofluorescein diacetate (DCFH-DA) assay revealed increased ROS production. Upon 3-(4-5-dimethylthiazol-2-yl)-2.5-dyhphenyltetrazolium bromide (MTT) assay, isoprene (IP), one of ingredients of CS, deceased JEG-3 cell viability (10-11 to 10-6 M). After based on the MTT assay, two IP concentrations of 10-11 and 10-8 M were selected and the protein expressions of cyclin D1, cyclin E1, p21, and p27 decreased in response to IP. Furthermore, IP showed the greatest increase in autophagy at 24 hours and further induction of cell death at 72 hours upon monodansylacadaverine and TUNEL assay. Western blot analysis confirmed the increase in autophagy markers, LC3β and p62, as well as the increase or decrease of apoptosis markers p53, Bax, CHOP, and Bcl-2 in response to its treatments. In addition to confirming increases in ROS through DCFH-DA, we also confirmed the expression of Nrf2, an antioxidant marker, and the expression of Kelch-like ECH-associated protein 1 (KEAP1), which specifically degrades Nrf2, by Western blot. Taken together, these results indicate that CS and IP may inhibit the development of placenta via activation of ROS by inducing apoptosis and autophagy by affecting the expression of KEAP1, which regulates Nrf2 expression.

Gene Expression Profiling in Human Lung Cells Exposed to Isoprene-Derived Secondary Organic Aerosol

Secondary organic aerosol (SOA) derived from the photochemical oxidation of isoprene contributes a substantial mass fraction to atmospheric fine particulate matter (PM2.5). The formation of isoprene SOA is influenced largely by anthropogenic emissions through multiphase chemistry of its multigenerational oxidation products. Considering the abundance of isoprene SOA in the troposphere, understanding mechanisms of adverse health effects through inhalation exposure is critical to mitigating its potential impact on public health. In this study, we assessed the effects of isoprene SOA on gene expression in human airway epithelial cells (BEAS-2B) through an air-liquid interface exposure. Gene expression profiling of 84 oxidative stress and 249 inflammation-associated human genes was performed. Our results show that the expression levels of 29 genes were significantly altered upon isoprene SOA exposure under noncytotoxic conditions (p < 0.05), with the majority (22/29) of genes passing a false discovery rate threshold of 0.3. The most significantly affected genes belong to the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) transcription factor network. The Nrf2 function is confirmed through a reporter cell line. Together with detailed characterization of SOA constituents, this study reveals the impact of isoprene SOA exposure on lung responses and highlights the importance of further understanding its potential health outcomes.

Genotoxicity of alkene epoxides in human peripheral blood mononuclear cells and HL60 leukaemia cells evaluated with the comet assay

Volatile organic compounds (VOCs) exert their carcinogenic activity through the production of epoxide metabolites. Because of their high reactivity some epoxides are also produced in the chemical industry for the synthesis of other compounds. Therefore, human exposure to VOCs epoxides does occur and may be an important human health concern. In this study, the in vitro genotoxic potential of epoxides originating from 1,3-butadiene (3,4-epoxy-1-butene: EB; 1,2:3,4-diepoxybutane: DEB), isoprene (3,4-epoxy-2-methyl-1-butene: IO), styrene (styrene-7,8-oxide: SO), propylene (propylene oxide: PO) and 1-butene (1,2-epoxy-butane: BO) in human peripheral blood mononuclear cells (PBMCs) and promyelocytic leukaemia cells (HL60) was measured with the comet assay (single-cell gel electrophoresis, SCGE). The effect of inclusion of foetal calf serum (FCS, 5%) in the cell-culture medium and different durations of exposure (2h, 24h) were also investigated. All epoxides tested produced DNA damage in a concentration range that did not reduce cell viability. HL60 cells were more resistant than PBMCs to the DNA damage induced by the different epoxides. With the exception of IO, the treatment for 24h resulted in an increase of DNA damage. FCS slightly protected PBMCs from the genotoxic effects induced by IO and BO, whilst no such effect was noted for the other compounds. Overall, the dose-dependent effects that were seen allowed us to define a genotoxicity scale for the different epoxides as follows: SO>EB>DEB>IO>PO>BO, which is in partial agreement with the International Agency for Research on Cancer (IARC) classification of the carcinogenic hazards.

Identification of isopentenol biosynthetic genes from Bacillus subtilis by a screening method based on isoprenoid precursor toxicity

We have developed a novel method to clone terpene synthase genes. This method relies on the inherent toxicity of the prenyl diphosphate precursors to terpenes, which resulted in a reduced-growth phenotype. When these precursors were consumed by a terpene synthase, normal growth was restored. We have demonstrated that this method is capable of enriching a population of engineered Escherichia coli for those clones that express the sesquiterpene-producing amorphadiene synthase. In addition, we enriched a library of genomic DNA from the isoprene-producing bacterium Bacillus subtilis strain 6,051 in E. coli engineered to produce elevated levels of isopentenyl diphosphate and dimethylallyl diphosphate. The selection resulted in the discovery of two genes (yhfR and nudF) whose protein products acted directly on the prenyl diphosphate precursors and produced isopentenol. Expression of nudF in E. coli engineered with the mevalonate-based isopentenyl pyrophosphate biosynthetic pathway resulted in the production of isopentenol.

DNA-damaging ability of isoprene and isoprene mono-epoxide (EPOX I) in human cells evaluated with the comet assay

Isoprene is produced in combustion processes and is widely used as an industrial chemical. It is a natural product emitted by plants and endogenously produced by humans and other mammals. Therefore, exposure to isoprene from both endogenous and exogenous sources is unavoidable and occurs during the entire human life. Based on evaluations of the International Agency for Research on Cancer (IARC), isoprene has been classified in Group 2B (possibly carcinogenic to humans). In the present work, we have demonstrated, by use of the single-cell gel electrophoresis assay (SCGE or comet assay), that isoprene is able to induce DNA damage in peripheral blood mononuclear cells (PBMCs) in the presence of metabolic activation. In addition, treatment of cells with the main isoprene mono-epoxide (EPOX I) induced time- and dose- dependent DNA damage in both PBMCs and human leukaemia cells (HL60). The metabolic activation system, represented by rat liver post-mitochondrial fractions (S9), was obtained from rats that had been treated - or not - with inducing agents such as phenobarbital and ethanol. The inclusion of S9 fractions (4mg protein/mL) from non-induced or phenobarbital-induced rats resulted in a statistically significant enhancement of isoprene genotoxicity. A different pattern was obtained by the addition of ethanol-induced S9, which appeared highly genotoxic by itself even in the absence of isoprene. Reducing the concentration of ethanol-induced S9 to 0.25mg protein/mL resulted in a considerable enhancement of isoprene genotoxicity. In the absence of clear epidemiological evidence of the carcinogenicity of isoprene in humans, the results of this study seem to be particularly important since they add new findings to support the classification of this chemical as possibly carcinogenic to humans.

Toxicology of 1,3-butadiene, chloroprene, and isoprene

The diene monomers, 1,3-butadiene, chloroprene, and isoprene, respectively, differ only in substitution of a hydrogen, a chlorine, or a methyl group at the second of the four unsaturated carbon atoms in these linear molecules. Literature reviewed in the preceding sections indicates that these chemicals have important uses in synthesis of polymers, which offer significant benefits within modern society. Additionally, studies document that these monomers can increase the tumor formation rate in various organs of rats and mice during chronic cancer bioassays. The extent of tumor formation versus animal exposure to these monomers varies significantly across species, as well among strains within species. These studies approach, but do not resolve, important questions of human risk from inhalation exposure. Each of these diene monomers can be activated to electrophilic epoxide metabolites through microsomal oxidation reactions in mammals. These epoxide metabolites are genotoxic through reactions with nucleic acids. Some of these reactions cause mutations and subsequent cancers, as noted in animal experiments. Significant differences exist among the compounds, particularly in the extent of formation of highly mutagenic diepoxide metabolites, when animals are exposed. These metabolites are detoxified through hydrolysis by epoxide hydrolase enzymes and through conjugation with glutathione with the aid of glutathione S-transferase. Different strains and species perform these reactions with varying efficacy. Mice produce these electrophilic epoxides more rapidly and appear to have less adequate detoxification mechanisms than rats or humans. The weight of evidence from many studies suggests that the balance of activation versus detoxification offers explanation of differing sensitivities of animals to these carcinogenic actions. Other aspects, including molecular biology of the many processes that lead through specific mutations to cancer, are yet to be understood. Melnick and Sills (2001) compared the carcinogenic potentials of these three dienes, along with that of ethylene oxide, which also acts through an epoxide intermediate. From the number of tissue sites where experimental animal tumors were detected, butadiene offers greatest potential for carcinogenicity of these dienes. Chloroprene and then isoprene appear to follow in this order. Comparisons among these chemicals based on responses to external exposures are complicated by differences among studies and of species and tissue susceptibilities. Physiologically based pharmacokinetic models offer promise to overcome these impediments to interpretation. Mechanistic studies at the molecular level offer promise for understanding the relationships among electrophilic metabolites and vital genetic components. Significant improvements in minimization of industrial worker exposures to carcinogenic chemicals have been accomplished after realization that vinyl chloride caused hepatic angiosarcoma in polymer production workers (Creech and Johnson 1974; Falk et al. 1974). Efforts continue to minimize disease, particularly cancer, from exposures to chemicals such as these dienes. Industry has responded to significant challenges that affect the health of workers through efforts that minimize plant exposures and by sponsorship of research, including animal and epidemiological studies. Governmental agencies provide oversight and have developed facilities that accomplish studies of continuing scientific excellence. These entities grapple with differences in perspective, objectives, and interpretation as synthesis of knowledge develops through mutual work. A major challenge remains, however, in assessment of significance of environmental human exposures to these dienes. Such exposure levels are orders of magnitude less than exposures studied in experimental or epidemiological settings, but exposures may persist much longer and may involve unknown but potentially significant sensitivities in the general population. New paradigms likely will be needed for toxicological evaluation of these human exposures, which are ongoing but as yet are not interpreted.

Hemoglobin adducts and micronuclei in rodents after treatment with isoprene monoxide or butadiene monoxide

1,3-Butadiene and isoprene (2-methyl-1,3-butadiene) are chemically related substances that are carcinogenic to rodents. The overall aim of this work is to elucidate the role of the genotoxic action of diepoxide metabolites in the carcinogenesis of the dialkenes. In vivo doses of the diepoxide metabolites were measured through reaction products with hemoglobin (Hb adducts) in studies of induced micronuclei (MN) in rodents. In the reaction with N-terminal valine in Hb, diepoxybutane and isoprenediepoxide form ring-closed adducts, pyrrolidines [N,N-(2,3-dihydroxy-1,4-butadiyl)valine and N,N-(2,3-dihydroxy-2-methyl-1,4-butadiyl)valine, respectively]. The method applied for Hb-adduct measurement is based on tryptic degradation of the protein and liquid chromatography electrospray ionisation tandem mass spectrometry (LC-ESI-MS/MS) analysis. Mice were given single i.p. injections of the monoepoxides of butadiene and isoprene, 1,2-epoxy-3-butene or 1,2-epoxy-2-methyl-3-butene, respectively. Rats were treated in the same way with 1,2-epoxy-3-butene. In mice pyrrolidine adduct levels increased with increasing administered doses of the monoepoxides. The in vivo dose of diepoxybutane was on average twice as high (0.29+/-0.059 mMh) as the in vivo dose of isoprenediepoxide (0.15+/-0.053 mMh) per administered dose (mmol/kg body weight) of the monoepoxides. In mice the genotoxic effects of the two monoepoxides, measured as the increase in the frequencies of micronuclei (MN), were approximately linearly correlated to the in vivo doses of the diepoxides (except at the highest dose of diepoxybutane). In rats the pyrrolidine-adduct levels from diepoxybutane were below the limit of quantification at all administered doses of 1,2-epoxy-3-butene and no significant increase was observed in the frequency of MN. Measurement of the ring-closed adducts to N-termini in Hb by the applied method permits analysis of in vivo doses of diepoxybutane and isoprenediepoxide, which may be further used for the elucidation of the mechanisms of carcinogenesis of butadiene and isoprene.

Effects of 1,3-butadiene, isoprene, and their photochemical degradation products on human lung cells

Because of potential exposure both in the workplace and from ambient air, the known carcinogen 1,3-butadiene (BD) is considered a priority hazardous air pollutant. BD and its 2-methyl analog, isoprene (ISO), are chemically similar but have very different toxicities, with ISO showing no significant carcinogenesis. Once released into the atmosphere, reactions with species induced by sunlight and nitrogen oxides convert BD and ISO into several photochemical reaction products. In this study, we determined the relative toxicity and inflammatory gene expression induced by exposure of A549 cells to BD, ISO, and their photochemical degradation products in the presence of nitric oxide. Gas chromatography and mass spectrometry analyses indicate the initial and major photochemical products produced during these experiments for BD are acrolein, acetaldehyde, and formaldehyde, and products for ISO are methacrolein, methyl vinyl ketone, and formaldehyde; both formed < 200 ppb of ozone. After exposure the cells were examined for cytotoxicity and interleukin-8 (IL-8) gene expression, as a marker for inflammation. These results indicate that although BD and ISO alone caused similar cytotoxicity and IL-8 responses compared with the air control, their photochemical products significantly enhanced cytotoxicity and IL-8 gene expression. This suggests that once ISO and BD are released into the environment, reactions occurring in the atmosphere transform these hydrocarbons into products that induce potentially greater adverse health effects than the emitted hydrocarbons by themselves. In addition, the data suggest that based on the carbon concentration or per carbon basis, biogenic ISO transforms into products with proinflammatory potential similar to that of BD products.

Safety evaluation of a triterpenoid-rich extract from bamboo shavings

Triterpenoids, which may have significant application to the development of natural medicines and functional foods as biological active components, are widely distributed throughout the plant kingdom. This paper evaluated the safety of a triterpenoid-rich extract of bamboo shavings (EBS) systematically. (i) Acute toxicity test: The oral maximum tolerated dose of EBS was more than 10 g/kg body weight both in rats and in mice, due to the absence of toxicity according to the criteria of acute toxic classifications. (ii) Mutagenicity test: It had no mutagenicity judged by negative experimental results of Ames test, mouse bone marrow cell micronucleus test and mouse sperm abnormality test. (iii) 30 days feeding study: No abnormal symptoms and clinical signs or deaths had been found in rats in each group during the test. No significant difference had been found in body weight, food consumption and food availability of rats in each test group (P>0.05). In addition, no significant differences were found in each hematology value, clinical chemistry value and organ/body weight ratio, either (P>0.05). No abnormality of any organ was found during histopathological examination. It can be concluded that the extract of bamboo shavings is of low toxicity and support the use of EBS for various foods.

Stereochemical and kinetic comparisons of mono- and diepoxide formation in the in vitro metabolism of isoprene by liver microsomes from rats, mice, and humans

Isoprene (2-methylbuta-1,3-diene) is a large scale petrochemical used principally in the manufacture of synthetic rubbers. It is also produced by plants and trees and is formed endogenously in mammals as a major endogenous hydrocarbon. Mammalian metabolism of isoprene involves cytochrome P450-dependent monooxygenases to give the regioisomeric monoepoxides, prop-2-enyloxirane and 2-ethenyl-2-methyloxirane. The isoprene monoepoxides are further oxidized to the mutagenic diepoxides, 2-methyl-2,2'-bioxiranes. The present studies have investigated the stereochemistry and comparative rates of the metabolic epoxidation in vitro of isoprene to mono- and diepoxides by liver microsomes from rat, mouse, and human in order to identify stereochemical and kinetic differences between species in the formation of these epoxide metabolites, which are key to understanding the toxicology of isoprene. The assignments of stereochemistry were based on comparisons with synthetic standards, the syntheses for which are described. Comparative enzyme kinetic parameters (apparent K(m) and apparent V(max) values) for the in vitro formation of all of the monoepoxide and diepoxide stereoisomers have been obtained. The rates of formation of both mono- and diepoxides were greater in the rodent systems as compared with the human in vitro system. The results provide comparative kinetic data that have potential for modeling and assessing the relevance of the animal carcinogenicity data for man. The possibility of human interindividual variation was also investigated with liver preparations from several individual humans, but significant differences between individuals were not observed in the formation of the monoepoxides from isoprene.

REPEATED EXPOSURE INHALATION STUDY OF PENTANE IN RATS

Pentane (CAS No. 109-66-0) is a chemical being used as a co-solvent in a polymer production facility with potential for inhalation exposure in humans. To assess the toxicity of pentane, groups of 10 male rats each were exposed by inhalation, 6 hr/day, 5 days/week for 2 weeks to either 0 (control), 1,000, 3,000 or 10,000 ppm. Five rats per group were killed following the 10th exposure; the remaining 5/group were killed after a 14-day post-exposure recovery period. Parameters investigated were clinical signs of toxicity, functional behavior, body weights, clinical pathology, and gross and microscopic pathology including organ weights. No unusual clinical observations were seen in the pentane-treated rats, and body weights were not altered. Test rats generally exhibited normal behavioral responses in the functional observational battery. Increases in serum calcium and phosphorus concentrations were seen in rats exposed to either 3,000 or 10,000 ppm. These were reversible during the 2-week recovery period. No other clinical pathology changes were observed and no pentane-related tissue pathology was seen in any of the groups. The no-observed-adverse-effect level was 1,000 ppm with reversible clinical pathology changes produced at 3,000 and 10,000 ppm.

A limited developmental toxicity study of pentane by inhalation in the rat

Pentane (CAS No. 109-66-0) is a widely-used chemical that finds many industrial applications. As part of a program looking at the inhalation toxicity of pentane, we studied the potential effects of the chemical on the developing embryo. This communication reports the findings of a limited study which was used to determine whether a full-scale developmental toxicity study was necessary. Groups of 7 to 8 pregnant rats were exposed by inhalation to pentane, 6 hr/day from gestation days 6 through 15 at concentrations of 0 (control), 1000, 3000 and 10,000 ppm, Maternal body weights, clinical signs and food consumption were measured; foetuses were weighed and examined for gross external development. Skeletal and internal organ evaluations were not performed. There were no effects in either the maternal or fetal rats (at concentrations up to and including 10,000 ppm) that could be associated with pentane exposure. Based on those findings, we did not conduct a full-spectrum developmental toxicity study in rats, but concluded that it is unlikely that the foetus would be adversely affected by pentane exposure.

Toxicology of n-pentane (CAS no. 109-66-0)

n-Pentane (CAS no. 109-6-0) is a hydrocarbon solvent with an estimated production volume of 50000 metric tons in Europe. The present work was carried out to strengthen the toxicological information available for regulatory decision-making, particularly product classification, occupational exposure limits and risk assessment. The work described in this report was sponsored either by the Pentane Special Interest Group under the auspices of the Hydrocarbon Solvent Producers Association of CEFIC (European Chemical Industry Council) or by Exxon Chemical Europe. The following results were obtained: n-pentane was not acutely toxic by oral or inhalation routes, it was not a skin or eye irritant and did not induce skin sensitization. It did not exhibit cumulative toxicity at levels up to 20000 mg m(-3), which is approximately one-half of the lower explosive limit and the highest level considered safe to test. It did not induce developmental toxicity and was not mutagenic. From this and other existing information, it is concluded that n-pentane does not require classification for potential toxic hazards (as defined by Annex VI of the EU Dangerous Substance Directive, 1993), although the physical properties indicate that it would be appropriate to warn for the potential for aspiration. Further, there is no reason to reduce the current occupational exposure recommendations. Finally, although there are some safety issues relating to the flammability of n-pentane, the absence of any demonstrable toxicity at high treatment levels indicates that the risk of adverse health effects is minimal for all segments of the population.

[Metabolism and toxicity of n-pentane and isopentane]

n-Pentane and isopentane have a wide range of use, for example, for cleaning precision machinery, extracting essence and oil, and as liquid fuel for now very popular disposable lighters. They are contained in liquefied petroleum gas and natural gas as trace constituents. In our present experiments, we studied the metabolism and toxicity of these n-pentane and isopentane metabolites. Male mice of ICR strain were exposed to about 5% n-pentane for one hour while the oxygen in the environmental air was maintained at about 20%. Then their blood and liver tissue were collected and analyzed by means of GC and GC-MS. The metabolites thus obtained were 2-pentanol, 3-pentanol and 2-pentanone. The same procedure was repeated with isopentane; 3-methyl-2-butanol, 2-methyl-2-butanol and 3-methyl-2-butanone were detected as the resultant metabolites. In the presence of the NADPH-generating system liver microsomes were made to react to the substrate of saturated n-pentane or isopentane aqueous solution at 37 degrees C for one hour. As a result, the same metabolites were produced as obtained in the exposure experiment. It was therefore suggested that n-pentane and isopentane were metabolized chiefly by liver microsomes. Male mice of ICR strain were fed with 80 mg/kg b.w. of phenobarbital for consecutive four days and exposed to n-pentane or isopentane for one hour. This resulted in an increase in the amount of 2-pentanol and 2-pentanone in the n-pentane inhalation and 2-methyl-2-butanol in the isopentane inhalation experiment. The toxicity of each metabolite was studied on cultured cells. The metabolites were individually mixed with HeLa S3 cell suspension, incubated for three days, and their concentration which inhibited the growth of cells by 50% (IGC 50) were compared. It was demonstrated as a result that the IGC 50 for any of the metabolites was lower than that for methanol, ethanol or acetone used as control.

A method for measuring nasal and lung uptake of inhaled vapor

This paper describes apparatus and methods for measuring uptake of inhaled vapors in the nose and lungs of dogs. The system allows sampling of air from the trachea at specific times during inspiration and expiration without surgical manipulation of the animal, thus allowing repeated studies in the same animal. During exposure, the dogs are anesthetized and cyclic respiratory patterns are maintained by means of an external respirator. A pneumotachograph installed in the exposure line is connected to a respiratory monitoring system that both monitors the dog's respiratory pattern and triggers sampling at specific times in the respiratory cycle. Air sampling, both at the nose and within the trachea, can be done during the entire breathing cycle or during specific portions of it. Vapors are sampled at a point just external to the dog's nose and from within the trachea through a modified endotracheal tube. To develop and demonstrate the system, three beagle dogs were exposed to 2,4-dimethylpentane and 1.3-dioxolane at nominal vapor concentrations of 500 ppm; vapor sampling was triggered for the entire inspiratory and expiratory portions of the breathing cycle during 10-min exposures. After correcting data to account for vapor that desorbed from the nasal passages during exhalation (after initially being absorbed in the nose during inhalation), net nasal uptake of 2,4-dimethylpentane was 28.3%; net nasal uptake of 1,3-dioxolane was 66.6%. Lung uptake was 14.0% for 2,4-dimethylpentane and 2.1% for 1,3-dioxolane. The system was developed for use with dogs, but it can be adapted for use with any animal species that can be intubated with endotracheal vapor sampling tubes.

Lack of detectable metabolism for solubilized 2,3,4-trimethylpentane by rat kidney proximal tubules

Primary proximal tubule suspension cultures exposed to solubilized 2,3,4-trimethylpentane (2,3,4-TMP) resulted in a linear dose response, as determined by cellular lactate dehydrogenase leakage. The EC50 for 2,3,4-TMP was 16.3 mM. Metabolite analysis by gas chromatography/mass spectrometry of supernate and cell extracts from cultures exposed to 2,3,4-TMP (12.0 mM) failed to detect the presence of metabolites. Electron-microscopic examination of proximal tubules exposed to 2,3,4-TMP indicated ultrastructural changes that included increased mitochondrial swelling, increased vesiculation, decreased microvilli and pyknotic nuclei. This study indicates that kidney proximal tubules do not appear to metabolize 2,3,4-TMP.

In vitro toxicity of solubilized 2,3,4-trimethylpentane. I. Cytotoxicity and metabolism of TMP using primary hepatocytes

Primary rat hepatocyte suspension cultures (approximately 2 X 10(6) cells) exposed to solubilized 2,3,4-trimethylpentane at concentrations ranging from 7.9 to 31.5 mM under two different culture conditions resulted in a linear dose response, as determined by lactate dehydrogenase leakage and viability data. A significant increase in the 2,3,4-trimethylpentane effective concentration 50 for primary hepatocytes occurred when exposures were implemented in medium containing 0.05% albumin. The effective concentration 50 for hepatocytes exposed to 2,3,4-trimethylpentane in medium lacking and containing albumin were 17.1 and 20.7 mM, respectively. Metabolite analysis by gas chromatography-mass spectrometry of supernatant (lacking or containing albumin) and cell extracts from hepatocyte cultures exposed to 2,3,4-trimethylpentane for 4 h indicated the presence of three metabolites: 2,3,4-trimethyl-1-pentanol, 2,3,4-trimethyl-2-pentanol, 2,3,4-trimethyl-2-pentanol, and 2,3,4-trimethyl-1-pentanoic acid. Electron microscopic examination of 2,3,4-trimethylpentane-exposed primary hepatocytes indicated ultrastructural changes which included abnormal condensed chromatin association with the nuclear membrane, swollen mitochondria, increased amounts of cytoplasmic lipid, significant loss of microvilli from the cell surface, increased vacuolation, and increased numbers of peroxisomes. Although these changes were observed under both culture conditions, they were more severe in cultures lacking albumin. This study indicates that primary hepatocyte suspension cultures provide a useful system for rapidly identifying liver metabolites of selected test compounds of interest.

Comparative toxicities of the naturally occurring nitrile 1-cyano-3,4-epithiobutane and the synthetic nitrile n-valeronitrile in rats: differences in target organs, metabolism and toxic mechanisms

Toxic but sublethal oral doses of 125 mg/kg (1.1 mmol/kg) of the cruciferous nitrile, 1-cyano-3,4-epithiobutane (CEB), or 175 mg/kg (2.1 mmol/kg) of its synthetic saturated analogue, n-valeronitrile (VN), were given by gavage to male CDF (F-344/CrlBr) rats once daily for 1, 2 or 3 days, in order to compare target tissues and to observe structure-activity relationships between the nitriles. CEB-induced changes included degeneration and necrosis of the pars recta of the renal proximal tubules, ulceration and necrosis in the forestomach, a mild increase (4.5-fold) in daily urinary thiocyanate (SCN-) excretion (only in rats treated for 3 days) and 1.5- to 2.4-fold increases in hepatic and pancreatic non-protein thiol (RSH) concentrations (in all CEB-treated groups). In VN-treated rats, there were no consistent histological changes but 95- to 170-fold increases in daily urinary SCN- excretion, delayed clinical signs of cyanide toxicity and minimal effects on tissue RSH concentrations. These results indicate different toxic mechanisms for VN and CEB. The nephrotoxic effects of CEB were very similar to those of 1-cyano-2-hydroxy-3,4-epithiobutane, suggesting a role for the epithio group in the nephrotoxicity of these nitriles. The relatively low SCN- excretion in CEB-treated rats also suggested that cyanide played only a minimal role in CEB toxicity, while the high SCN- excretion, clinical signs of cyanide poisoning and lack of histological changes imply a greater role for metabolically-derived cyanide in VN toxicity. The enhancement of tissue RSH by CEB treatment with indications of enhanced tissue glutathione concentrations suggested the involvement of glutathione in the detoxication of CEB and/or its reactive metabolites.

Identification of urinary metabolites in rats exposed to the nephrotoxic agent 2,3,4-trimethylpentane

Branched-chain hydrocarbon-induced nephropathy in male rats was examined using 2,3,4-trimethylpentane. Lesions are elected only in male rats, not in females or in controls. Mechanisms of nephropathy may be the interaction of metabolites with the male rat-specific protein alpha 2u globulin. The identified urinary metabolites of 2,3,4-trimethylpentane in male rats given the hydrocarbon by gavage are 2,3,4-trimethyl-1-pentanol, 2,3,4-trimethyl-2-pentanol and 2,3,4-trimethyl-1-pentanoic acid. Of the C8-isomers, 2,3,4-trimethylpentane dosing leads to the highest incidence of kidney damage in male rats.

A method for the continuous measurement of respiration and vapor uptake in rats

A method for determining the uptake of inhaled vapors in rats is described. The method uses gas chromatographic data to enable calculations of vapor concentration differences upstream and downstream from a rat exposed to the vapor by the nose-only route. Respiratory data are recorded simultaneously. The data can be used to determine the rate of uptake, uptake as a fraction of vapor inhaled and the effects of vapor inhalation on respiration.

[Neurotoxic workshop materials: II. Organic substances--a review of the years 1970 to 1982]

This paper summarizes the knowledge and recent research of some organic neurotoxic substances at the workplace concerning peripheral nervous system. The review covers the substances: acrylamide, n-hexane, methyl-n-butylketone, n-pentane, n-heptane, carbondisulfide, styrene, toluene, trichloroethylene, tri-ortho-cresylphosphate and other organophosphorus compounds, polyhalogenated and complex organic compounds and solvent-mixtures. First the chemical and physical properties, the toxicokinetic and biotransformation as well as possibilities of exposure at the workplace are given. Following the characteristics after acute and chronic intoxications. The effects to the peripheral nervous systems due to short- and longtime exposure of the substance are described. Field studies in exposed workers and neurophysiological investigations with evaluation of dose-effect-relationships are reviewed especially. Each section is discussed and evaluated in respect to occupational medicine.

A comparative study on the neurotoxicity of n-pentane, n-hexane, and n-heptane in the rat

The neurotoxicity of n-pentane, n-hexane, and n-heptane have been studied in Wistar strain male rats after exposure to 3000 ppm of n-pentane, n-hexane, or n-heptane for 12 hours a day for 16 weeks. The nerve conduction velocity and the distal latency were measured before the beginning of the exposure and after exposure for four, eight, 12, and 16 weeks. The experiment showed that n-hexane disturbed the conduction velocity of the motor nerve and the mixed nerve and prolonged the distal latency in the rat's tail, but that n-pentane and n-heptane did not. The light and electron microscopic examination showed that the peripheral nerve, the neuromuscular junction, and the muscle fibre of the rats exposed to n-hexane were severely impaired, but those of the rats exposed to n-pentane or n-heptane showed no particular changes even after 16 weeks of exposure. These results show that n-hexane is far more toxic to the peripheral nerve of the rat than n-pentane or n-heptane. It is necessary to study the neurotoxicity of other petroleum hydrocarbons, since some reports suggest that petroleum solvents might possibly contain neurotoxic hydrocarbons other than n-hexane.