Human inhalation exposure to ethylene glycol.

Two male volunteers (A and B) inhaled 1.43 and 1.34 mmol, respectively, of vaporous 13C-labeled ethylene glycol (13C2-EG) over 4 h. In plasma, 13C2-EG and its metabolite 13C2-glycolic acid (13C2-GA) were determined together with the natural burden from background GA using a gas chromatograph equipped with a mass selective detector. Maximum plasma concentrations of 13C2-EG were 11.0 and 15.8 µmol/l, and of 13C2-GA were 0.9 and 1.8 µmol/l, for volunteers A and B, respectively. Corresponding plasma half-lives were 2.1 and 2.6 h for 13C2-EG, and 2.9 and 2.6 h for 13C2-GA. Background GA concentrations were 25.8 and 28.3 µmol/l plasma. Unlabeled background EG, GA and oxalic acid (OA) were detected in urine in which the corresponding 13C-labeled compounds were also quantified. Within 28 h after the start of the exposures, 6.4% and 9.3% 13C2-EG, 0.70% and 0.92% 13C2-GA, as well as 0.08% and 0.28% 13C2-OA of the inhaled amounts of 13C2-EG, were excreted in urine by volunteers A and B, respectively. The amounts of 13C2-GA represented 3.7% and 14.2% of background urinary GA excreted over 24 h (274 and 88 µmol). The amounts of 13C2-OA were 0.5% and 2.1% of background urinary OA excreted over 24 h (215 and 177 µmol). From the findings obtained in plasma and urine and from a toxicokinetic analysis of these data, it is highly unlikely that workplace EG exposure according to the German exposure limit (MAK-value 10 ppm EG, 8 h) could lead to adverse effects from the metabolically formed GA and OA

Kinetics of propylene oxide metabolism in microsomes and cytosol of different organs from mouse, rat, and humans.

Kinetics of the metabolic inactivation of 1,2-epoxypropane (propylene oxide; PO) catalyzed by glutathione S-transferase (GST) and by epoxide hydrolase (EH) were investigated at 37 degrees C in cytosol and microsomes of liver and lung of B6C3F1 mice, F344 rats, and humans and of respiratory and olfactory nasal mucosa of F344 rats. In all of these tissues, GST and EH activities were detected. GST activity for PO was found in cytosolic fractions exclusively. EH activity for PO could be determined only in microsomes, with the exception of human livers where some cytosolic activity also occurred, representing 1-3% of the corresponding GST activity. For GST, the ratio of the maximum metabolic rate (V(max)) to the apparent Michaelis constant (K(m)) could be quantified for all tissues. In liver and lung, these ratios ranged from 12 (human liver) to 106 microl/min/mg protein (mouse lung). Corresponding values for EH ranged from 4.4 (mouse liver) to 46 (human lung). The lowest V(max) value for EH was found in mouse lung (7.1 nmol/min/mg protein); the highest was found in human liver (80 nmol/min/mg protein). K(m) values for EH-mediated PO hydrolysis in liver and lung ranged from 0.83 (human lung) to 3.7 mmol/L (mouse liver). With respect to liver and lung, the highest V(max)/K(m) ratios were obtained for GST in mouse and for EH in human tissues. GST activities were higher in lung than in liver of mouse and human and were alike in both rat tissues. Species-specific EH activities in lung were similar to those in liver. In rat nasal mucosa, GST and EH activities were much higher than in rat liver

Molecular dosimetry of N7-(2-hydroxypropyl)guanine in tissues of F344 rats after inhalation exposure to propylene oxide.

Propylene oxide (PO) is a high-volume chemical intermediate that causes a low incidence of nasal tumors in rodents exposed to high concentrations (≥300 p.p.m.). PO reacts with DNA forming mainly N7-(2-hydroxypropyl)guanine (7-HPG). The exposure-dependent accumulation of 7-HPG in nasal respiratory epithelium (NRE), lung and liver was determined in male F344 rats exposed to PO (0, 5, 25, 50, 300 or 500 p.p.m.) by the inhalation route for 3 or 20 days (6 h/day; 5 days/week). These exposures ranged from low concentrations, such as those potentially occurring in the workplace, to high concentrations that proved to be carcinogenic in rodents. Analysis of 7-HPG in DNA by gas chromatography–high-resolution mass spectrometry (GC–HRMS) showed a linear response in 7-HPG for all three tissues after 3 days of exposure, and for NRE and lung after 20 days of exposure. A slightly sublinear response in 7-HPG was observed in liver after 20 days of exposure. For both exposure periods, the NRE had the highest concentration of 7-HPG, followed by lung and liver. The amount of 7-HPG in NRE was seven and 17 times higher than in lung and liver, respectively, for the 3 day exposures. For the 20 day exposures, the concentration of 7-HPG in NRE was six and 13 times higher than that in lung and liver, respectively, over the concentration range studied. These results demonstrate a much higher extent of DNA alkylation in the target tissue for carcinogenesis, than in non-target tissues. As PO-induced tumor formation was highly sublinear, occurring only at high vapor concentrations, whereas 7-HPG adducts were shown to be linearly dependent on airborne concentration, these results suggest that 7-HPG is not sufficient for PO nasal carcinogenesis and that other factors such as increased cell proliferation may be important in determining the tumor exposure response

First-pass metabolism of 1,3-butadiene in once-through perfused livers of rats and mice.

First-pass metabolism of 1,3-butadiene (BD) leading to 1,2-epoxy-3-butene (EB), 1,2:3,4-diepoxybutane (DEB), 3-butene-1,2-diol (B-diol), 3,4-epoxy-1,2-butanediol (EBD) and crotonaldehyde (CA) was studied quantitatively in the once-through BD perfused liver of mouse and rat by means of an all-glass gas-tight perfusion system. Metabolites were analyzed using gas chromatography equipped with mass selective detection. The perfusate consisted of Krebs-Henseleit buffer (pH 7.4) containing bovine erythrocytes (40%v/v) and BD. The perfusion flow rates through the livers were 3-4 ml/min (mouse) and 17-20 ml/min (rat). The BD concentrations in the liver perfusates were 330 nmol/ml (mouse) and 240 nmol/ml (rat) being high enough to reach almost saturation of BD metabolism. The mean rates of BD transformation were about 0.014 and 0.055 mmol/h per liver of a mouse and a rat, respectively, being similar to the values expected from in-vivo measurements. There were marked species differences in the formation of BD metabolites. In the effluent of mouse livers, all three epoxides (EB: 9.4 nmol/ml; DEB: 0.06 nmol/ml; EBD: 0.07 nmol/ml) and B-diol (8.2 nmol/ml) were detected. In the perfusate leaving naïve rat livers, only EB and B-diol were found. In that of rat liver, EB concentration was 8.5 times smaller than in that of mouse liver, whereas B-diol concentrations were similar in the effluent liver perfusate of both species. CA was below the limit of its detection (60 nmol/l) in the liver perfusate of mice and of naïve rats. Of BD metabolized, the sum of the metabolites investigated in the effluent amounted to only 30% (mouse) and 20% (rat). In first experiments with rat liver, glutathione (GSH) was depleted by pretreating the animals with diethylmaleate. With the exception of EBD (not quantifiable due to an interfering peak), all other metabolites including CA were found in the effluent perfusate summing up to about 70 and 100% of BD metabolized, which indicates the quantitative importance of the GSH dependent metabolism. In summary, the results demonstrate the relevance of an intrahepatic first-pass metabolism for metabolic intermediates of BD, which undergo further transformation immediately after their production in the liver before leaving this organ. Hitherto, the occurrence of this first-pass metabolism was only hypothesized. The findings will help to explain the drastic species difference between mice and rats in the carcinogenic potency of BD

Quantitation of DNA and hemoglobin adducta and apurinic/apyrimidinic sites in tissue of F344 rats exposed to propylene oxide by inhalation.

Propylene oxide (PO) is a relatively weak mutagen that induces nasal tumor formation in rats during long-term inhalation studies at high exposures (≥300 p.p.m.), concentrations that also cause cytotoxicity and increases in cell proliferation. Direct alkylation of DNA by PO leads mainly to the formation of N7-(2-hydroxypropyl)guanine (7-HPG). In this study, the accumulation of 7-HPG in tissues of male F344 rats exposed to 500 p.p.m. PO (6 h/day, 5 days/week for 4 weeks) by the inhalation route was measured by gas chromatography–high resolution mass spectrometry (GC-HRMS). In animals killed up to 7 h following the end of the last exposure the levels of 7-HPG (pmol/μmol guanine) in nasal respiratory tissue, nasal olfactory tissue, lung, spleen, liver and testis DNA were 606.2 ± 53.0, 297.5 ± 56.5, 69.8 ± 3.8, 43.0 ± 3.8, 27.5 ± 2.4 and 14.2 ± 0.7, respectively. The amounts of 7-HPG in the same tissues of animals killed 3 days after cessation of exposure were 393.3 ± 57.0, 222.7 ± 29.5, 51.5 ± 1.2, 26.7 ± 1.0, 18.0 ± 2.6 and 10.4 ± 0.1. A comparable rate of disappearance of 7-HPG was found among all tissues. DNA from lymphocytes pooled from four rats killed at the end of the last exposure was found to have 39.6 pmol adduct/μmol guanine. Quantitation of DNA apurinic/apyrimidinic sites, potentially formed after adduct loss by chemical depurination or DNA repair, showed no difference between tissues from control and exposed rats. The level of N-(2-hydroxypropyl)valine in hemoglobin of exposed rats was also determined using a modified Edman degradation method followed by GC-HRMS analysis. The value obtained was 90.2 ± 10.3 pmol/mg globin. These data demonstrate that nasal respiratory tissue, which is the target tissue for carcinogenesis, has a much greater level of alkylation of DNA than non-target tissues

Inhalation and epidermal exposure of volunteers to ethylene glycol: Kinetics of absorption, urinary excretion, and metabolism to glycolate and oxalate.

Ethylene glycol (EG) is a widely used liquid. Limited data are published regarding inhaled EG and no data regarding transdermal EG uptake in humans. In order to gain information on the quantitative fate of EG, four male volunteers inhaled between 1340 and 1610mumol vaporous (13)C-labeled EG ((13)C(2)-EG) for 4h. Separately, three of these subjects were epidermally exposed for up to 6h to liquid (13)C(2)-EG (skin area 66cm(2)). Plasma concentrations and urinary amounts of (13)C(2)-EG were determined by gas chromatography with mass selective detection. Additionally, plasma was assayed for (13)C-labeled glycolic acid ((13)C(2)-GA) and urine for (13)C(2)-GA and (13)C-labeled oxalic acid ((13)C(2)-OA). Both EG metabolites were nephrotoxic in animals and humans and embryotoxic in rodents. (13)C-labels enabled to differentiate from also determined endogenous EG, glycolic acid (GA), and oxalic acid (OA). Of (13)C(2)-EG inhaled, 5.5+/-3.0%, 0.77+/-0.15%, and 0.10+/-0.12% were detected in urine as (13)C(2)-EG, (13)C(2)-GA, and (13)C(2)-OA, respectively. The skin permeability constant of liquid EG was 2.7x10(-5)+/-0.5x10(-5)cm/h. Of the dose taken up transdermally, 8.1+/-3.2% and up to 0.4% were excreted in urine as (13)C(2)-EG and (13)C(2)-GA, respectively. It is calculated that equally long-lasting exposure to 10ppm vaporous EG or wetting of both hands by liquid EG leads to about the same body burden by EG and metabolites. The amounts of GA and OA excreted daily in urine as a result of exposure (8h/day) to 10ppm EG are about 15% and 2%, respectively, of those excreted from naturally occurring endogenous GA and OA

Concentrations of the propylene metabolite propylene oxide in blood of propylene-exposed rats and humans--a basis for risk assessment.

Propylene (PE) was not carcinogenic in long-term studies in rodents. However, its biotransformation to propylene oxide (PO) raises questions about a carcinogenic risk. PO alkylates macromolecules, is a direct mutagen, and caused tumors in rodents at high concentrations. In order to acquire knowledge on the species-specific PO concentrations in blood resulting from PE exposure, we exposed male Fischer 344/N rats in closed exposure chambers to constant PE concentrations, between 20.1 and 3000 ppm (7 h at least), and four male volunteers to mean constant PE concentrations of 9.82 and 23.4 ppm (180 min) in inhaled air. In the animal experiments, PE and PO were measured in the chamber atmosphere, PE by gas chromatography with flame ionization detection (GC/FID), PO by GC/FID or GC with mass-selective detection (GC/MSD). In the human studies, PE was measured in inhaled and exhaled air by GC/FID. PO was quantified by GC/MSD from exhaled breath collected in gasbags. Blood concentrations of PO were calculated based on the measured PO concentrations in air using the blood-to-air partition coefficients of 60 (rat) and 66 (human). In rats, PO blood concentrations ranged from 53 nmol/l at 20.1 ppm PE to 1750 nmol/l at 3000 ppm PE. In humans, mean blood concentrations of PO were 0.44 and 0.92 nmol/l at mean PE concentrations of 9.82 and 23.4 ppm, respectively. These findings should be taken into consideration when estimating the carcinogenic risk of PE to humans based on carcinogenicity studies in PE- or PO-exposed rats