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W Dekant

Publications and source records attributed to W Dekant.

At least 19 recordsLinked to original sources
PubMed2006

Biotransformation and pharmacokinetics of the antiplasmodial naphthylisoquinoline alkaloid dioncophylline A.

The biotransformation of the antiplasmodial naphthylisoquinoline alkaloid dioncophylline A by rat liver microsomes and its pharmacokinetics in male rats were studied. Incubation of dioncophylline A with rat liver microsomes resulted in the formation of the major metabolite 5'-O-demethyldioncophylline A, and a second minor metabolite, corresponding to the mass of an as yet unknown 4-hydroxydioncophylline A. Kinetic constants of the formation of 5'-O-demethyldioncophylline A were Km = 32 nmol and Vmax = 20 pmol min-1 mg-1). Administration of dioncophylline A at a dose of 6.67 mg kg-1 body weight to rats intravenously and orally (n = 4 per group) resulted in peak plasma levels of 0.84 and 0.11 microg ml-1, respectively. Levels of metabolites were below the limit of quantitation (LOQ). The following pharmacokinetic parameters of dioncophylline A were determined: oral bioavailability of 25%, plasma half-life of 2.5 h and partition volume of 8 l kg-1 body weight. Concentrations of dioncophylline A metabolites in all plasma and urine samples were below the limit of detection (LOD) and recovery of dioncophylline A in urine was very low, suggesting distribution into lipid rich tissues.

Administration, Oral↗
PubMed2005

Reaction of nitroso derivatives of dinitropyrenes with sulfhydryl groups of peptides and hemoglobin in vitro and in rats.

Diesel engine emissions have been classified as a potential human carcinogen and may cause a variety of other health effects. Human exposure to diesel engine emissions is highly variable within the population. Therefore, specific methods for the biomonitoring of human exposure to diesel engine emissions are required for exposure assessment within epidemiological studies. Haemoglobin adducts of dinitropyrenes may serve as biomarkers for human exposures to diesel engine emissions.To characterize structures of dinitropyrene reaction products with sulfhydryl groups, glutathione was used to trap electrophilic nitroso intermediates formed from dinitropyrenes and glutathione S-conjugates were identified and characterized by Qtrap techniques using (HPLC-MS/MS) high-performance liquid chromatography coupled to triple quadrupole mass spectrometry. Nitrosonitropyrene-derived sulfinamides, sulfenamides and glutathione thioethers bound to carbon atoms in the aromatic ring, presumably formed by a rearrangement of intermediate sulfenamide cations, were formed in low yields. In haemoglobin from rats orally administered dinitropyrenes, mild alkaline hydrolysis of haemoglobin released aminonitropyrenes, which were identified by HPLC-MS/MS. The results demonstrate that dinitropyrenes undergo nitroreduction in rats and that the intermediate nitrosonitropyrenes bind to heamoglobin. The haemoglobin adducts formed from dinitropyrenes seem, in contrast to previous studies, to be hydrolysable and thus represent sulfen- and sulfinamides derived from the intermediate nitrosonitropyrenes. The developed Qtrap methods to detect and characterize glutathione S-conjugates rapidly may have wide applications in attempts to characterize reactive intermediates formed in complex mixtures in low concentrations.

Air Pollutants↗
PubMed2001

Neoantigen formation and clastogenic action of HCFC-123 and perchloroethylene in human MCL-5 cells.

In this study, the metabolic activation of 2,2-dichloro-1,1,1-trifluoroethane (hydrochlorofluorocarbons-123, HCFC-123), halothane or 1,1-dichloro-1-fluoroethane (HCFC-141b) was compared to that of perchloroethylene, using lymphoblastoma derived cell lines expressing human CYP1A1, CYP1A2, CYP2E1, CYP2A6 and CYP3A4 (MCL-5 cells). A dose dependent increase in micronucleus formation was detected over a nominal concentration range of 0.05-2 mM for HCFC-123 and halothane, but this was not seen with HCFC-141b. No dose response for HCFC-123 was seen in a control cHo1 cell line not expressing this cytochrome P450's. Cell lines expressing individual human cytochrome P-450 (CYP) forms were also used to define the enzymes responsible for the clastogenic events and to investigate the formation of immunoreactive protein by microsomal fractions. It was shown that CYP2E1 or CYP2B6 catalysed the clastogenic response, but CYP2D6, CYP3A4, CYP1A2 or CYP1A1 all appeared to be inactive. The formation of neoantigenic trifluoroacetylated protein adducts by microsomal mixtures incubated with HCFC-123 and NADPH was catalysed primarily by CYP2E1 and to a lesser extent by CYP2C19, whereas, only trace levels of immunoreactive protein were seen with microsomes expressing CYP2B6 or CYP2C8. With perchloroethylene as a substrate, the extent of activation was low in comparison with HCFC-123, as judged by the absence of micronuclei formation in the MCL-5 cell line and the weak immunoreactivity of proteins following Western blotting. CYP1A2, CYP2B6 and CYP2C8 appeared to be responsible for perchloroethylene immunoreactivity and in contrast to the findings with the HCFC's, no activation of perchloroethylene by CYP2E1 could be detected. These results show that even though both saturated and unsaturated halocarbons can result in neoantigen formation, there is a marked difference in the specificity of the CYP enzymes involved in their metabolic activation.

Antigens↗
PubMed2001

Toxicokinetics of ethers used as fuel oxygenates.

The toxicokinetics and biotransformation of methyl-tert.butyl ether (MTBE), ethyl-tert.butyl ether (ETBE) and tert.amyl-methyl ether (TAME) in rats and humans are summarized. These ethers are used as gasoline additives in large amounts, and thus, a considerable potential for human exposure exists. After inhalation exposure MTBE, ETBE and TAME are rapidly taken up by both rats and humans; after termination of exposure, clearance by exhalation and biotransformation to urinary metabolites is rapid in rats. In humans, clearance by exhalation is slower in comparison to rats. Biotransformation of MTBE and ETBE is both qualitatively and quantitatively similar in humans and rats after inhalation exposure under identical conditions. The extent of biotransformation of TAME is also quantitatively similar in rats and humans; the metabolic pathways, however, are different. The results suggest that reactive and potentially toxic metabolites are not formed during biotransformation of these ethers and that toxic effects of these compounds initiated by covalent binding to cellular macromolecules are unlikely.

Air Pollutants↗
PubMed2001

Chemical-induced nephrotoxicity mediated by glutathione S-conjugate formation.

Glutathione conjugation has been identified as an important detoxication reaction. However, several glutathione-dependent bioactivation reactions have been identified. Current knowledge on the mechanisms and the possible biological importance of these reactions is discussed in this article. Vicinal dihaloalkanes are transformed by glutathione S-transferase-catalyzed reactions to mutagenic and nephrotoxic S-(2-haloethyl) glutathione S-conjugates. Electrophilic episulphonium ions are the ultimate reactive intermediates formed and interact with nucleic acids. Several polychlorinated alkenes are bioactivated in a complex, glutathione-dependent pathway. The first step is hepatic glutathione S-conjugate formation followed by cleavage to the corresponding cysteine S-conjugates, and, after translocation to the kidney, metabolism by renal cystein conjugate beta-lyase. Beta-Lyase-dependent metabolism of halovinyl cysteine S-conjugates yields electrophilic thioketenes, whose covalent binding to cellular macromolecules is likely to be responsible for the observed nephrotoxicity of the parent compounds. Finally, hepatic glutathione conjugate formation with hydroquinones and aminophenols yields conjugates that are directed to gamma-glutamyltransferase-rich tissues, such as the kidney, where they cause alkylation or redox cycling reactions, or both, that cause organ-selective damage.

Alkanes↗
PubMed2001

Ochratoxin A-induced tumor formation: is there a role of reactive ochratoxin A metabolites?

Ochratoxin A is a nephrotoxic and tumorigenic mycotoxin which contaminates a variety of food items, resulting in chronic human exposure. Biotransformation reactions have been implicated in the tumorigenicity of ochratoxin A. The biotransformation of ochratoxin A by cytochromes P450 and other mammalian enzymes was investigated to optimize conditions for bacterial mutagenicity testing. Metabolite formation was assessed by HPLC with UV and fluorescence detection and by LC/MS/MS. When ochratoxin A was incubated with liver microsomes from rats and mice, formation of 4R- and 4S-hydroxyochratoxin A was observed at very low rates. However, oxidation of ochratoxin A was not observed using kidney microsomes from rats and mice. Significantly higher rates of oxidation were seen in liver microsomes from rats pretreated with 3-methylcholanthrene and dexamethasone. Other reported or postulated that ochratoxin A-metabolites were not formed in detectable concentrations. Human cytochromes P450 (3A4, 1A2, and 2C9-1 Supersomes((R))) also showed very low activity with ochratoxin A (<60 fmole/min x pmol P450). Other enzyme systems used to study possible biotransformation of ochratoxin A were rat and human liver and kidney S-9 fortified with NADPH and glutathione, semipurified glutathione S-transferases, horseradish peroxidase, and soybean lipoxygenase; none of these resulted in detectable biotransformation of ochratoxin A. Using rat liver microsomes with high activity for ochratoxin A oxidation and the other enzyme systems to activate ochratoxin A for mutagenicity testing in the Ames test, mutagenicity was not observed in Salmonella typhimurium TA 100 and TA 2638. The obtained results suggest that oxidative biotransformation of ochratoxin A occurs at low rates, is catalyzed by cytochromes P450, and is unlikely to form reactive intermediates capable of binding to DNA.

Animals↗
PubMed2001

Toxicokinetics of methyl tert-butyl ether and its metabolites in humans after oral exposure.

Methyl tert-butyl ether (MTBE) is widely used as an additive to gasoline, to increase oxygen content and reduce tailpipe emission of pollutants. Widespread human exposure to MTBE may occur due to leakage of gasoline storage tanks and a high stability and mobility of MTBE in ground water. To compare disposition of MTBE after different routes of exposure, its biotransformation was studied in humans after oral administration in water. Human volunteers (3 males and 3 females, identical individuals, exposures were performed 4 weeks apart) were exposed to 5 and 15 mg 13C-MTBE dissolved in 100 ml of water. Urine samples from the volunteers were collected for 96 h after administration in 6-h intervals and blood samples were taken in intervals for 24 h. In urine, MTBE and the MTBE-metabolites tert-butanol (t-butanol), 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were quantified, MTBE and t-butanol were determined in blood samples and in exhaled air in a limited study of 3 male volunteers given 15 mg MTBE in 100 ml of water. MTBE blood concentrations were 0.69 +/- 0.25 microM after 15 mg MTBE and 0.10 +/- 0.03 microM after 5 mg MTBE. MTBE was rapidly cleared from blood with terminal half-lives of 3.7 +/- 0.9 h (15 mg MTBE) and 8.1 +/- 3.0 h (5 mg MTBE). The blood concentrations of t-butanol were 1.82 +/- 0.63 microM after 15 mg MTBE and 0.45 +/- 0.13 microM after 5 mg MTBE. Approximately 30% of the MTBE dose was cleared by exhalation as unchanged MTBE and as t-butanol. MTBE exhalation was rapid and maximal MTBE concentrations (100 nmol/l) in exhaled air were achieved within 10-20 min. Clearance of MTBE by exhalation paralleled clearance of MTBE from blood. T-butanol was cleared from blood with half-lives of 8.5 +/- 2.4 h (15 mg MTBE) and 8.1 +/- 1.6 h (5 mg MTBE). In urine samples, 2-hydroxyisobutyrate was recovered as major excretory product, t-butanol and 2-methyl-1,2-propane diol were minor metabolites. Elimination half-lives for the different urinary metabolites of MTBE were between 7.7 and 17.8 h. Approximately 50% of the administered MTBE was recovered in urine of the volunteers after both exposures, another 30% was recovered in exhaled air as unchanged MTBE and t-butanol. The obtained data indicate that MTBE-biotransformation and excretion after oral exposure is similar to inhalation exposure and suggest the absence of a significant first-pass metabolism of MTBE in the liver after oral administration.

Adult↗
PubMed2001

A physiologically based pharmacokinetic model for methyl tert-butyl ether in humans: implementing sensitivity and variability analyses.

Methyl tert-butyl ether (MTBE) is added to gasoline to reduce carbon monoxide and ozone precursors from automobile emissions. The objectives of this study were to verify the ability of a physiologically based pharmacokinetic (PBPK) model to predict MTBE blood levels in humans and to investigate the effect of variability in the metabolism of MTBE and its influence on the predicted MTBE blood levels. The model structure for MTBE was flow-limited and had six essential compartments: lung, liver, rapidly perfused tissues, slowly perfused tissues, fat, and kidney. In this model, two pathways of metabolism are described to occur in the liver by Michaelis-Menten kinetics. Metabolic rate constants were measured in vitro using human liver microsomes and extrapolated to in vivo whole-body metabolism. Model predictions were compared with data on blood levels of MTBE taken from humans during and after a 1-h inhalation exposure to 1.7 ppm MTBE and after 4-h inhalation exposures to 4 or 40 ppm MTBE. The PBPK model accurately predicted MTBE pharmacokinetics at the high and low MTBE exposure concentrations for all time points. At the intermediate MTBE exposure concentration, however, the model underpredicted early time points while adequately predicting later time points. Results of the sensitivity analysis indicated that the influence of metabolic parameters on model output was dependent on MTBE exposure concentration. Subsequent variability analysis indicated that there was more variability in the actual measured MTBE blood levels than in the blood levels predicted by the PBPK model when using the range of metabolic parameters measured in vitro in human liver samples. By incorporating an understanding of the metabolic processes, this PBPK model can be used to predict blood levels of MTBE, which is important in determining target tissue dose estimates for risk assessment.

Administration, Inhalation↗
PubMed2001

Disposition and biotransformation of the estrogenic isoflavone daidzein in rats.

Daidzein is an estrogenic isoflavone present in many plants and therefore consumed in relatively high doses by humans. Daidzein has a low affinity for the estrogen receptor (3 orders of magnitude lower than estradiol) and has been demonstrated to have estrogenic effects in rodents after administration of high doses. We have studied the disposition and biotransformation of daidzein in rats fed a diet low in isoflavone content. Four male and four female Fischer 344 rats were orally administered 100 mg/kg daidzein; excreted urine and feces were collected for 96 h and unchanged daidzein as well as formed metabolites were quantified by HPLC. In urine of male rats, daidzein, daidzein-glucuronide, and daidzein-sulfate were excreted; in females, only unchanged daidzein and daidzein-glucuronide were present. Total urinary excretion of daidzein accounted for < 10% of dose in both males and females. The major pathway of daidzein elimination was excretion of unchanged daidzein with feces. Reductive daidzein-metabolites likely formed by intestinal microflora (equol, O-desmethylangolensin) were excreted with feces in small amounts (< 5% of dose). Excretion of daidzein and metabolites with urine and feces was rapid with elimination half-lives of less than 12 h; daidzein concentrations in urine and feces were below the limit of detection 36 h after daidzein administration. The results suggest that daidzein is only poorly absorbed from the gastrointestinal tract in rodents. Absorbed daidzein is rapidly eliminated both unchanged and as conjugates with urine. The inefficient absorption of daidzein from the gastrointestinal tract and the rapid excretion may explain the weak estrogenicity of daidzein seen in vivo in rodents when compared to other estrogenic chemicals with comparatively low affinity to the estrogen receptor.

Animals↗
PubMed2001

Biotransformation of MTBE, ETBE, and TAME after inhalation or ingestion in rats and humans.

The biotransformation of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) was studied in humans and in rats after inhalation of 4 and 40 ppm of MTBE, ETBE, and TAME, respectively, for 4 hours, and the biotransformation of MTBE and TAME was studied after ingestion exposure in humans to 5 and 15 mg in water. tert-Butyl alcohol (TBA), a TBA conjugate, 2-methyl-1,2-propanediol, and 2-hydroxyisobutyrate were found to be metabolites of MTBE and ETBE. tert-Amyl alcohol (TAA), free and glucuronidated 2-methyl-2,3-butanediol (a glucuronide of TAA), 2-hydroxy-2-methyl butyrate, and 3-hydroxy-3-methyl butyrate were found to be metabolites of TAME. After inhalation, MTBE, ETBE, and TAME were rapidly taken up by both rats and humans; after termination of exposure, clearance from blood of the ethers by exhalation and biotransformation to urinary metabolites occurred with half-times of less than 7 hours in rats and humans. Biotransformation of MTBE and ETBE was similar in humans and rats after inhalation exposure. 2-Hydroxyisobutyrate was recovered as a major product in urine. All metabolites of MTBE and ETBE excreted with urine were eliminated with half-times of less than 20 hours. Biotransformation of TAME was qualitatively similar in rats and humans, but the metabolic pathways were different. In humans, 2-methyl-2,3-butanediol, 2-hydroxy-2-methyl butyrate, and 3-hydroxy-3methyl butyrate were recovered as major urinary products. In rats, however, 2-methyl-2,3-butanediol and its glucuronide were major TAME metabolites recovered in urine. After ingestion of MTBE and TAME, both compounds were rapidly absorbed from the gastrointestinal tract. Hepatic first-pass metabolism of these ethers was not observed, and a significant part of the administered dose was transferred into blood and cleared by exhalation. Metabolic pathways for MTBE and TAME and kinetics of excretion were identical after ingestion and inhalation exposures. Results of studies presented here suggest (1) that excretion of MTBE, ETBE, and TAME in rats and humans is rapid, (2) that biotransformation and excretion of MTBE and ETBE are identical in rats, and (3) that biotransformation and excretion of TAME is quantitatively different in rats and humans.

Administration, Oral↗
PubMed2000

Structural improvement of higher education in environmental toxicology in Latin America and Europe.

Industrial development has resulted in an increased release of chemicals and other agents into the environment, resulting in damage to the environment as well as increasing the risk of adverse effects on human health. Environmental toxicology (ET) is the discipline responsible for assessing the risks to human health and the environment from the effects of new chemicals and those already present in the environment. The development of human resources in toxicology is therefore a priority in both Latin America (LA) and the European Union (EU), although LA professionals are more involved in risk evaluation than in risk assessment compared to their EU colleagues. A solid background in general toxicology will enable those interested in environmental issues to tackle local problems. Moreover, the increasing globalization of markets and, therefore, of the necessary regulations, requires harmonisation of postgraduate programmes to ensure that risk assessment and management related to the environment are dealt with uniformly and by highly qualified scientists. The Inaugural Meeting of the ALFA-OMET Toxicology', a 2-year programme supported by the European Commission, offered the opportunity to discuss a number of these issues. The present status of existing ET courses in the EU and LA and the corresponding professional profiles in the two regions were examined, and a harmonized academic curriculum for a postgraduate professional profiles in the two regions were examined, and a harmonized academic curriculum for a postgraduate course in environmental toxicology was developed. Finally, a course programme for toxicology and a specialization in environmental toxicology designed by a panel of experts was discussed, and its relevance as a model for other specialisation programmes was analysed. Exercises such as those performed by ALFA-OMET may be useful not only in promoting discussion for the implementation of national and international professional registers in LA, but also in encouraging the same, ongoing process in the EU.

Environmental Pollutants↗
PubMed2000

Biotransformation and male rat-specific renal toxicity of diethyl ethyl- and dimethyl methylphosphonate.

Dimethyl methylphosphonate (DMMP) is a widely used chemical. Diethyl ethylphosphonate (DEEP) has been proposed as a replacement for DMMP in several applications. A long-term carcinogenesis study with DMMP in rats and mice showed a significant increase in the incidence of kidney tumors after 2 years of exposure in male but not in female rats and both sexes of mice. DMMP is not genotoxic. Due to these findings, a role of alpha(2u)-globulin accumulation in organ-specific tumorigenicity may be possible. alpha(2u)-Globulin is a low-molecular-weight protein synthesized in male rats under androgen control. Several male rat specific renal carcinogens have been shown to bind to alpha(2u)-globulin and to impair the renal degradation of this protein. This impairment results in alpha(2u)-globulin accumulation in the kidney, lysosomal overload, cell death, cell proliferation, and finally, renal tumor induction. To further characterize the toxicology of DMMP and DEEP, we investigated the biotransformation of these compounds and their ability to induce alpha(2u)-globulin accumulation in kidney. Biotransformation of both DMMP and DEEP were studied in male and female rats after single oral doses of 50 and 100 mg/kg. 31P-NMR and GC/MS showed that unchanged DMMP was excreted with urine; methyl phosphonate was identified as the only metabolite in urine. Unchanged DEEP was also excreted with urine; in addition, ethyl ethylphosphonate and ethylphosphonate were urinary metabolites. The majority of the applied dose of both compounds was recovered in urine within 24 h indicating rapid absorption and excretion. No sex-differences in rates of formation or excretion of metabolites were seen. To investigate alpha(2u)-globulin accumulation in the kidney after DMMP and DEEP, male and female Fischer-344 rats were administered DMMP or DEEP daily for five consecutive days by gavage. DMMP doses were 500- and 1,000-mg/kg body weight (bw); due to marked toxicity, daily DEEP dose of 50 and 100 mg/kg had to be used. Control rats received corn oil only and positive controls received five doses of 500-mg/kg bw trimethylpentane (TMP). Relative kidney weights were increased in male rats dosed with DMMP, DEEP, and TMP. alpha(2u)-Globulin in kidney cytosol was separated and quantified by capillary electrophoresis and by SDS-PAGE and Western blotting. In DMMP-, DEEP-, and TMP-treated rats, dose-dependent increases in the alpha(2u)-globulin content were observed by both methods in male, but not female rats. The increase of alpha(2u)-globulin accumulation was accompanied by the formation of protein droplets in the proximal tubules of male rats. These data demonstrate that the sex specific increase in kidney tumors by DMMP in male rats may be due to alpha(2u)-globulin accumulation and that similar toxic effects are to be expected from DEEP.

Administration, Oral↗
PubMed2000

Biotransformation and kinetics of excretion of ethyl tert-butyl ether in rats and humans.

Ethyl tert-butyl ether (ETBE) may be used in the future as an additive to gasoline to increase oxygen content and reduce tailpipe emissions of pollutants. Therefore, widespread human exposure may occur. To contribute to the characterization of potential adverse effects of ETBE, its biotransformation was compared in humans and rats after inhalation exposure. Human volunteers (3 males and 3 females) and rats (5 males and 5 females) were exposed to 4 (4.5+/-0.6) and 40 (40.6+/-3.0) ppm ETBE for 4 h in a dynamic exposure system. Urine samples from rats and humans were collected for 72 h at 6-h intervals, and blood samples were taken in regular intervals for 48 h. In urine, ETBE and the ETBE-metabolites tert-butanol (t-butanol), 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were quantified; ETBE and t-butanol were determined in blood samples. After the end of the exposure period to inhalation of 40-ppm ETBE, blood concentrations of ETBE were found at 5.3+/-1.2 microM in rats and 12.1+/-4.0 microM in humans. The ETBE blood concentrations, after inhalation of 4-ppm ETBE, were 1.0+/-0.7 microM in rats and 1.3+/-0.7 microM in humans. ETBE was rapidly cleared from blood. After the end of the 40-ppm ETBE exposure period, the blood concentrations of t-butanol were 13.9+/-2.2 microM in humans and 21.7+/-4.9 microM in rats. After 4-ppm ETBE exposure, blood concentrations of t-butanol were 1.8+/-0.2 microM in humans and 5.7+/-0.8 microM in rats. t-Butanol was cleared from human blood with a half-life of 9.8+/-1.4 h in humans after 40-ppm ETBE exposure. In urine samples from controls and in samples collected from the volunteers and rats before the exposure, low concentrations of t-butanol, 2-methyl-1,2-propane diol, and 2-hydroxyisobutyrate were present. In the urine of both humans and rats exposed to ETBE, the concentrations of these compounds were significantly increased. 2-Hydroxy-isobutyrate was recovered in urine as the major excretory product formed from ETBE; t-butanol and 2-methyl-1,2-propane diol were minor metabolites. All metabolites of ETBE excreted with urine were rapidly eliminated in both species after the end of the ETBE exposure. Excretion half-lives for the different urinary metabolites of ETBE were between 10.2 and 28.3 h in humans and 2.6 and 4.7 h in rats. The obtained data indicate that ETBE biotransformation and excretion are similar for rats and humans, and that ETBE and its metabolites are rapidly excreted by both species. Between 41 and 53% of the ETBE retained after the end of the exposure was recovered as metabolites in the urine of both humans and rats.

Administration, Inhalation↗
PubMed2000

Biotransformation and kinetics of excretion of tert-amyl-methyl ether in humans and rats after inhalation exposure.

tert-Amyl methyl ether (TAME) may be widely used as an additive to gasoline in the future. The presence of this ether in gasoline reduces the tail pipe emission of pollutants. Therefore, widespread human exposure to TAME may occur. To contribute to the characterization of potential adverse effects of TAME, its biotransformation was compared in humans and rats after inhalation exposure. Human volunteers (three males and three females) and rats (five males and five females) were exposed to 4 (3.8 +/- 0.2) and 40 (38.4 +/- 1.7) ppm TAME for 4 h in a dynamic exposure system. Urine samples were collected for 72 h in 6-h intervals and blood samples were taken at regular intervals for 48 h in humans. In urine, the TAME metabolites tert-amyl alcohol (t-amyl alcohol), 2-methyl-2, 3-butane diol, 2-hydroxy-2-methylbutyric acid, and 3-hydroxy-3-methylbutyric acid were quantified. TAME and t-amyl alcohol were determined in blood samples. After the end of the exposure period, blood concentrations of TAME were 4.4 +/- 1.7 microM in humans and 9.6 +/- 1.4 microM in rats after 40 ppm TAME, and 0.6 +/- 0.1 microM in humans and 1.4 +/- 0.8 microM in rats after 4 ppm. TAME was rapidly cleared from blood in both rats and humans. The blood concentrations of t-amyl alcohol were 9.2 +/- 1.8 microM in humans and 8.1 +/- 1.5 microM in rats after 40 ppm TAME, and 1.0 +/- 0.3 microM in humans and 1.8 +/- 0.2 microM in rats after 4 ppm TAME. t-Amyl alcohol was also rapidly cleared from blood. In urine of humans, 2-methyl-2,3-butane diol, 2-hydroxy-2-methylbutyric acid, and 3-hydroxy-3-methylbutyric acid were recovered as major excretory products in urine. In rats, 2-methyl-2,3-butane diol and its glucuronide were major TAME metabolites. t-Amyl alcohol and its glucuronide were minor TAME metabolites in both species. All metabolites of TAME excreted with urine in rats were rapidly eliminated, with elimination half-lives of less than 6 h. Metabolite excretion in humans was slower and elimination half-lives of the different metabolites were between 6 and 40 h in humans. The obtained data indicate differences in TAME biotransformation and excretion between rats and humans. In rats, TAME metabolites are rapidly excreted. In humans, metabolic pathways are different and metabolite excretion is slower. Recovery of TAME metabolites in urine was higher in humans as compared to rats, suggesting more intensive biotransformation of TAME in humans.

Administration, Inhalation↗
PubMed1999

Gas chromatography-negative ion chemical ionization mass spectrometry as a powerful tool for the detection of mercapturic acids and DNA and protein adducts as biomarkers of exposure to halogenated olefins.

The studies on metabolism of halogenated olefins presented here outline the advantages of modern mass spectrometry. The perchloroethene (PER) metabolite N-acetyl-S-(trichlorovinyl)-L-cysteine (N-ac-TCVC) is an important biomarker for the glutathione dependent biotransformation of PER. In urine of rats and humans exposed to PER, N-ac-TCVC was quantified as methyl ester after BF3-MeOH derivatization by gas chromatography with chemical ionization and negative ion detection mass spectrometry (GC-NCI-MS). The detection limit was 10 fmol/microliter injected solution using [2H3]N-ac-TCVC methyl ester as the stable isotope internal standard. Cleavage of S-(trichlorovinyl)-L-cysteine by beta-lyase enzymes results in an electrophilic and highly reactive thioketene which reacts with nucleophilic groups in DNA and proteins. Protein adduct formation was shown in kidney mitochondria by identification of dichloroacetylated lysine after derivatization with 1,1,3,3-tetrafluoro-1,3-dichloroacetone by GC-NCI-MS. In addition, chlorothioketene was generated in organic solvents and reacted with cytosine to give N4-chlorothioacetyl cytosine. After derivatization with pentafluorobenzyl bromide this compound exhibited good gas chromatographic properties and was detectable with a limit of detection of 50 fmol/injected volume. The detection of chemically induced protein modifications in the target organ of toxic metabolite formation and the study of DNA modifications with chemically generated metabolites provide important information on organ toxicity and possible tumorigenicity of halogenated olefins.

Acetylcysteine↗
PubMed1999

Quantitation of N epsilon-(dichloroacetyl)-L-lysine in proteins after perchloroethene exposure by gas chromatography-mass spectrometry using chemical ionization and negative ion detection followingimmunoaffinity chromatography.

An antibody specific to N epsilon-(dichloroacetyl)-L-lysine (DCA-Lys) was immobilized to immunoaffinity columns for the use in selective enrichment of dichloroacetylated proteins. These result from the reaction with dichlorothioketene the beta-lyase cleavage product of the perchloroethene metabolite S-(trichlorovinyl)-L-cysteine. Dichloroacetylated proteins from rat kidney mitochondria, rat plasma and human blood plasma were isolated after exposure to 40 ppm tetrachloroethene (PER) for 6 h. After acid hydrolysis of the protein fraction, DCA-Lys was derivatized with 1,3-dichloro-1,1,3,3-tetrafluoroacetone using N epsilon-(trifluoroacetyl)-L-lysine as internal standard. Recovery of dichloroacetylated reference proteins from immunoaffinity columns was about 73%. Samples were analyzed by GC-MS with chemical ionization and negative ion (NCI) detection showing DCA-Lys in proteins with 2.26 (+/- 0.02) pmol/mg protein in male rat kidney mitochondria and 1.92 (+/- 0.05) pmol/mg total mitochondrial protein in female rats. In rat plasma 0.47 (+/- 0.006) pmol DCA-Lys/mg protein in male and 0.34 (+/- 0.02) in female animals were found. DCA-Lys could not be detected in blood plasma of human volunteers exposed to PER with a detection limit of 20 fmol for the DCA-Lys derivative 2,2-bis(chlorodifluoromethyl)-4-(1-dichloroacetamido)-butyl- 1,3-oxazolidine-5-one. Immunoaffinity chromatography with specific antibodies provides a powerful tool for the enrichment of minor quantities of dichloroacetyled proteins in biological samples for GC-NCI-MS analysis of the modified amino acid lysine having broad utility in the biomonitoring of PER exposure.

Adult↗